UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS. 

COLLEGE  OF  AGRICULTURE. 

AGRICULTURAL  EXPERIMENT  STATION. 


THE  BROWN  ROT  OF  THE  LEMON. 

By  RALPH  E.  SMITH. 

Assisted  by  H.  J.  Ramsey,  E.  H.  Smith,  E.  B.  Babcock  and  C.  O.  Smith. 


■ 

5^2 

BULLETIN    No.    190 

(Berkeley,  Cal.,  July,  1907.) 


W.    W.    SHANNON, 


SACRAMENTO: 

:     :     :     :     :     superintendent  state  printing, 
1907. 


BENJAMIN   IDE  WHEELER.   Ph.D.,   LL.D..  President  of  the   University. 


EXPERIMENT     STATION     STAFF. 

E.   J.   WICKSON,   M.A..   Acting  Director  and   Horticulturist. 

E.  W.   HILGARD.  Ph.D..  LL.D..  Chemist. 

W.    A.    SETCHELiIi,   Ph.D..   Botanist. 

ELWOOD  MEAD.  M.S.,  C.E..  Irrigation  Engineer. 

C     W.    WOODWORTH,   M.S.,   Entomologist. 

R.    H.    LOUGHRIDGE,    Ph.D..    Agricultural    Geologist    and    Soil    Physicist.       (Soils, 

Alkali.)  '    . 

M.  E.  JAFFA,  M.S.,  Nutrition  Expert,  in  charge  of  the  Poultry  Station. 
G.  W.  SHAW.  M.A..  Ph.D.,  Agricultural  Technologist,  in  charge  of  Cereal  Stations. 
GEORGE  E.  COLBY,  M.S.,  Chemist.      (Emits,  Waters,  Insecticides.) 
RALPH  E.  SMITH,  B.S.,  Plant  Pathologist  and  Superintendent  of  Southern  California 

Pathological  Laboratory  and  Experiment   Stations. 
A.  R.  WARD,  B.S.A.,  D.V.M.,   Veterinarian  and  Bacteriologist. 

E.  W.  MAJOR,   B.Agr.,  Animal  Industry  and  Manager  of  University  Farm. 

F.  T.   BIOLETTI,  M.S.,   Viticulturist.      (Grapes,   Wine  and  Zymology.) 
H.   M.   HALL.   M.S.,  Assistant  Botanist. 

H.   J.   QL'AYLE,  A.B.,   Assistant  Entomologist. 

W.    T.    CLARKE,    B.S.,    Assistant    Horticulturist    and    Superintendent    of    University 

Extension  in  Agriculture. 
JOHN  S.  BURD,  B.S.,  Chemist,  in  charge  of  Fertiliser  Control. 
C.  M.  HARING,  D.V.M.,  Assistant  Veterinarian  and  Bacteriologist. 
E.   B.   BABCOCK,  B.S.,  Assistant  Plant  Pathologist. 
E.  H.  SMITH,  M.S.,  Assistant  Plant  Pathologist. 

J.    W.    MILLS,    Assistant    Horticulturist,    j      CUrus  Experiment  8tatio7i,   Riverside. 

T.   F.   HUNT,   B.S.,      "  "  \ 

H.   J.  RAMSEY,  M.S.,  Assistant  Plant  Pathologist,  {    Southern  California  Pathologi- 

C.    O.    SMITH,    M.S.,  "  "  "  \         cal  Laboratory.     Whittier. 

R.  E.  MANSELL,  Assistant  in  Horticulture,  in  charge  of  Central  Station  Grounds. 

GEO.   W.   LYONS,  B.S.,   Assistant  in  Soil  Laboratory. 

RALPH  BENTON,   B.S.,  Assistant  in  Entomology. 

A.  J.   GAUMNITZ,  M.S.,  Assistant  in  Cereal  Investigations. 

HANS  C.   HOLM,  B.S.,  Assistant  in  Zymology. 

P.   L.   McCREART?,  B.S.,  Laboratory  Assistant  in  Fertilizer  Control. 

C.  WESTERGARD,   B.S.,   Assistant  in  Farm  Mechanics. 

M.  E.   STOVER,  B.S.,  Assistant  in  Agricultural  Chemical  Laboratory. 

D.  L.  BUNNELL,  Clerk  to  the  Director. 


JOHN  TUOHY,  Patron,  I  Tulare  Substation,  Tulare. 

J.   T.   BEARSS,  Foreman,  S 

J.  W.  ROPER,  Patron,  )  University  Forestry  Station,  Chico. 

E.   C.   MILLER,  In  charge,        ) 

ROY  JONES,   Patron,  1          University  Forestry  Station,  Santa  Monica. 

N.   D.   INGHAM,   Foreman,  \ 

VINCENT     J.     HUNTLEY  Foreman     of     California     Poultry     Experiment     Station, 
Petaluma. 

The  Station  publications  I  Reports  and  Bulletins),  so  long  as  avail- 
able, "ill  },,  sent  to  any  citizen  of  the  State  on  application. 


Digitized  by  the  Internet  Archive 

in  2012  with  funding  from 

University  of  California,  Davis  Libraries 


http://www.archive.org/details/brownrotoflemon190smit 


THE  BROWN  ROT  Of  THE  LEMON. 


By    RALPH   E.    SMITH. 
Assisted  by  H.  J.  Ramsey,  E.  H.  Smith,  E.  B.  Babcock,  and  C.  O.  Smith. 


The  subject  of  this  bulletin  is  a  peculiarly  virulent,  rapid-spreading 
form  of  decay  of  lemons  occurring  in  southern  California.  It  has  been 
named  "Brown  Rot"  by  the  growers  in  distinction  from  the  ordinary 
"Blue  Mould"  rot  caused  by  the  Penicillium  fungus,  the  usual  form 
of  decay  in  citrus  fruit.  Great  losses  have  been  experienced  from  this 
source  during  the  past  few  years,  and  it  has  remained  for  this  investi- 
gation to  determine  the  cause  and  means  of  control  of  the  trouble. 

The  history  of  the  lemon  industry  in  California  has  been  one  of  much 
vicissitude  and  uncertainty,  and  has  been  marked  particularly  by  a 
decidedly  sudden  and  apparently  permanent  change  from  a  condition 
of  deep  depression  and  discouragement  to  one  of  unusual  profit  and 
prosperity.  This  change  came  about  most  largely  during  the  season  of 
1904-05,  and  was  so  complete  as  to  transform  the  whole  aspect  of  the 
business. 

The  California  lemon  as  a  commercial  product  has  had  a  poor  repu- 
tation in  the  markets  of  the  country,  which  it  has  only  recently  begun 
to  live  down.  The  defect  has  been  in  keeping  quality,  in  which  respect 
the  native  product,  as  compared  with  imported  fruit,  has  been  notably 
deficient.  The  reasons  for  this  may  have  been  several,  but  for  present 
purposes  it  need  simply  be  said  that  by  improvements  in  their  methods 
of  handling  the  fruit  the  lemon  growers  and  shippers  of  the  State, 
taking  advantage  of  the  improved  market  conditions  brought  about  by 
the  short  foreign  crop  of  1904-05,  have  largely  overcome  the  prejudice 
against  the  keeping  quality  of  the  California  lemon,  and  are  doing  so 
more  and  more  with  every  car  that  leaves  the  State.  Supported  by  the 
abnormally  high  prices  of  the  last  three  seasons,  our  lemon  industry  has 
improved  and  strengthened  itself  all  along  the  line  to  a  really  remark- 
able extent.  Under  the  influence  of  the  leaders  of  the  industry  methods 
of  both  production  and  handling  have  been  improved,  the  cooperative 
selling  associations  have  strengthened  and  improved  their  condition 
and  enlarged  the  scope  of  their  influence,  and  the  whole  lemon  industry 
has  entered  upon  a  period  in  which  there  is  nothing  but  encouragement 
for  the  future. 


L  UNIVERSITY    OF   CALIFORNIA — EXPERIMENT  STATION. 

Excessive  decay,  in  curing,  transit,  and  on  the  market  has  been  the 
great  trouble  with  the  California  lemon  which  has  kept  it  from  enjoying 
the  appreciation  of  its  otherwise  excellent  qualities  to  which  it  is 
properly  entitled.     The  tree  is  peculiar  in  that  it  produces  fruit  at  all 

-  -nns  of  the  year,  which  fruit  is  not  allowed  to  mature  naturally  on 
the  tree  to  normal  ripeness  and  size,  but  is  picked  in  a  green  condition 
on  reaching  a  certain  size  and  then  stored  for  some  time  (several  weeks 
or  months     to  cure  or  ripen.     A  well-cured  lemon  does  not  rot.     It  can 

-  rcely  be  made  to  decay.  When  the  skin  has  been  dried  out  to  the 
ideal  firm  texture,  thinness  and  yellow  color,  under  the  proper  con- 
ditions of  atmospheric  moisture  for  good  curing,  the  lemon  can  be  kept 
for  months  without  decaying,  until  it  has  completely  dried  up  and 
mummified. 

It  has  been  demonstrated  that  most  of  the  decay  which  often  occurs 
so  extensively  during  the  period  from  the  tree  to  the  consumer,  and 
which  formerly  was  nearer  the  rule  than  the  exception  in  many  houses. 
is  directly  traceable  to  bruising  of  the  fruit  caused  by  rough  handling 
in  the  field  and  packing  house;  likewise  that  by  careful  handling  this 
rot  can  be  almost  entirely  eliminated.  One  of  the  greatest  advances  of 
the  California  lemon  industry  has  come  about  through  the  recognition 
of  this  simple  fact.  Decay  of  this  sort  is  commonly  caused  by  the 
so-called  ''Blue  Mould"  fungus,  species  of  Penicillium,  a  fungus  which 
is  not  particularly  active  as  a  parasite,  but  which  is  ever  ready  to  attack 
and  quickly  causes  the  decay  of  citrus  fruit  which  has  been  bruised  or 
weakened  in  any  way.  Penicillium  is  the  ever  present,  and,  until 
recently,  the  only  recognized  cause  of  citrus  decay  in  this  State.*  The 
recent  improvement  in  the  lemon  industry  just  referred  to  has  come 
about  largely  by  the  simple  exercise  of  more  care  in  handling  the  fruit 
to  prevent  bruising,  and  by  improved  methods  of  curing. 

Going  back  for  a  period  of  five  or  six  years  it  has  gradually  come 
about  that  the  lemon  people  have  begun  to  recognize  that  some  further 
(factor  than  the  ordinary  blue  mould  which  they  knew  how  to  handle 
causing  decay  of  their  fruit.  As  early  as  the  season  of  1901  the 
more  observant  of  them  had  come  to  the  conclusion  that  something 
entirely  distinct  from  the  ordinary  Penicillium  rot,  or  at  any  rate,  from 
their  standpoint,  a  different  proposition  for  handling,  was  confronting 
them.  This  fact  was  recognized  earliest  by  the  leaders  in  the  business. 
since  they  were  handling  ordinary  decay  successfully  and  could  quickly 
recognize  a  new  condition,  while  in  the  less  carefully  conducted  houses 
the  usual  amount  of  decay  up  to  a  very  recent  period  was  so  great 
that  a  new  cause  coming  in  had  little  effect  upon  the  general  average 

Wood  worth,  Orange  and  Lemon  Rot.     Bull.  139,  Cal.  Agr'l  Expt.  Sta. 
Powell,  The   Handling  of  Fruit  for  Transportation.     Year  Book  U.   S.  Dept.  of 
Agr.,  1905. 


Bulletin  190.  brown  ROT  OF  THE  LEMON.  3 

or  upon  the  minds  of  those  in  charge.  When,  however,  in  the  best 
houses,  the  shrinkage  between  picking  and  packing  rose  from  10  to  20 
or  30  per  cent,  when  an  amount  of  fruit  equal  to  10  per  cent  of  the 
entire  output  rotted  in  the  house  and  was  thrown  away  from  a  cause 
different  from  anything  encountered  in  previous  experience,  when  a 
large  amount  of  extra  help  was  constantly  required  in  handling  the 
fruit  in  order  to  keep  down  losses  to  even  these  abnormally  high 
amounts,  when  fruit  in  transit  decayed  in  an  inexplicable  manner  and 
to  an  unheard  of  extent,  and  when  the  losses  by  decay  in  single  houses 
rose  to  from  ten  to  thirty  thousand  dollars  per  year  above  that  which 
could  be  accounted  for  by  any  known  cause,  then  it  became  evident  that 
something  of  an  unusual  nature  was  going  on,  and  that  something 
must  be  done  to  meet  this  situation  or  the  lemon  business  would  again 
go  back  into  a  condition  of  depression  and  uncertainty. 

This  was  what  actually  occurred  in  many  houses  in  southern  Cali- 
fornia during  the  period  from  1901  to  1905.  Excessive  decay  occurred, 
whole  pickings  or  entire  lots  of  fruit  were  lost  in  some  cases,  and, 
except  that  something  new  and  peculiar  was  at  work,  practically  nothing 
Avas  known  as  to  the  cause  or  remedy  of  the  trouble.  Some  main- 
tained that  the  decay  was  nothing  more  than  a  severe  attack  of  the 
ordinary  blue-mould  fungus,  but  the  most  observant  of  those  who 
handled  the  fruit  soon  became  convinced  that  this  was  not  the  case. 

In  the  spring  of  1905  the  "Lemon  Men's  Club,"  an  organization  of 
the  leaders  in  the  California  lemon  business,  brought  this  matter  to  the 
attention  of  the  State  Experiment  Station.  Arrangements  were  made 
between  Mr.  C.  C.  Teague  of  the  Limoneira  Lemon  Company  and  the 
writer  for  commencing  an  investigation  of  the  trouble,  and  a  financial 
contribution  was  made  by  the  members  of  the  club  to  assist  in  the  work. 
The  investigation  was  inaugurated  by  placing  two  assistants  in  the 
field,  one  at  the  Limoneira  Ranch  at  Santa  Paula,  and  one  at  Whittier, 
working  at  the  latter  place  in  conjunction  with  Mr.  C.  W.  Leffingwell, 
Jr.,  and  the  Whittier  Citrus  Association.  A  large  share  of  the  credit 
for  whatever  good  may  have  come  from  this  work  is  due  to  the  above 
companies,  for  furnishing  fruit,  labor  and  many  facilities  and  conveni- 
ences for  carrying  on  our  experiments.  The  work  has  continued  con- 
stantly since  the  beginning  in  the  field,  packing  house  and  laboratory, 
most  of  the  lemon  packing  houses  of  southern  California  contributing, 
in  greater  or  less  degree  as  called  upon,  to  the  progress  of  the  work. 
It  is  with  a  feeling  of  more  than  ordinary  appreciation  that  the  writer 
acknowledges  the  support  given  to  this  investigation  by  the  lemon 
industry  of  southern  California.  In  the  fall  of  1905  a  temporary 
laboratory  was  established  at  Whittier,  through  the  courtesy  of  the 
Chamber  of  Commerce  of  that  city,  since  which  time  most  of  the  experi- 


4  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION. 

mental  work  has  been  done  at  that  place,  combined  with  extensive 
orchard  and  packing-house  demonstrations  in  other  sections.  Most  of 
the  experimental  and  field  work  of  the  investigation  has  been  carried 
out  by  Messrs.  11.  J.  Ramsey,  E.  B.  Babcock  and  C.  O.  Smith,  especially 
the  first  named,  while  the  study  of  the  fungus  in  the  laboratory  has 
Dived  largely  upon  Miss  E.  H.  Smith. 


METHODS   OF   GROWING   AND   HANDLING   LEMONS. 

It  will  be  necessary  to  give  a  brief  consideration  to  this  subject  for 
the  better  understanding  of  what  is  to  follow.  The  lemon,  like  other 
citrus  fruits,  is  an  evergreen  tree  of  semi-tropic  habit,  somewhat  more 
easily  affected  by  frost  than  the  orange.  As  already  stated  the  tree  is 
peculiar  in  producing  its  fruit  all  the  year  round;  that  is  to  say,  at 
almost  any  time  in  the  year  mature  fruit,  blossoms,  and  fruit  in  all 
stages  of  development  may  be  found  on  the  same  tree.  (See  cover 
illustration.)  Inasmuch  as  winter  is  the  usual  season  of  maturity  of 
citrus  fruits,  a  time  when  lemons  are  least  in  demand,  this  is  a  very 
valuable  feature.  There  is  a  tendency  to  produce  the  bulk  of  the  crop 
in  winter  and  spring,  especially  in  some  varieties  like  the  Lisbon,  which 
feature  is  not  at  all  desirable  from  the  standpoint  of  the  grower. 

PICKING. 

Lemons  allowed  to  mature  and  color  on  the  tree  become  overgrown, 
rough,  misshapen,  thick-skinned,  of  poor  keeping  quality  and  deficient 
in  acid.  One  of  the  principal  faults  of  the  California  lemon  on  the 
market  has  been  due  to  irregular  picking  and  allowing  the  fruit  to  get 
too  old  on  the  tree.  In  well-conducted  orchards  pickings  are  made 
once  a  month  or  at  the  longest  every  six  weeks.  The  selection  is  made 
by  means  of  a  ring  of  2*4  inches  diameter  (or  at  times  a  little  more 
or  less  .  all  lemons  which  will  not  pass  through  the  ring  being  picked. 
Smaller  ones  which  have  matured,  colored  and  ceased  growing  are 
also  taken.  The  most  desirable  fruit  is  that  which  is  of  moderate  size, 
unetrical  shape  and  dark  green  color.  The  lemons  are  cut  from  the 
Tr^e  by  means  of  clippers,  placed  in  a  sack  carried  by  the  picker,  emptied 
into  a  field  box  and  then  carried  to  the  packing  house.  In  all  these 
operations  the  greatest  care  is  necessary  not  to  cut  or  bruise  the  fruit  in 
any  manner. 

WASHING. 

It  is  at  present  the  almost  universal  practice  in  California  to  wash  all 
Lemons  as  soon  as  they  come  from  the  orchard.    The  practice  originated 


Bulletin  190. 


BROWN   ROT    OF   THE   LEMON. 


from  the  necessity  of  washing  decidedly  dirty  fruit,  especially  that 
which  was  affected  by  scale  insects  or  the  black,  sooty  fungus  which 
follows  their  attacks.  But  the  washing  of  even  the  cleanest  fruit  when 
green  is  so  beneficial  to  its  appearance  after  curing,  giving  it  a  gloss 
and  finish  not  seen  in  the  cleanest  unwashed  fruit,  and  the  process  is  so 
inexpensive,  that  washing  is  now  a  routine  process  in  lemon  handling 
without  regard  to  the  original  condition  of  the  fruit.  This  washing  is 
done  in  most  of  the  houses  with  the  machine  shown  in  figure  1.  This 
consists  of  a  sheet  iron  tank  of  the  shape  shown,  containing  a  circular 
arrangement  of  fixed  brushes  in  the  round  portion,  with  an  inner  circle 


PIG  1.     Usual   form  of  lemon  washer. 
(Photo  by  L.   B.   Williams.) 

of  brushes  which  revolves  rapidly  when  the  machine  is  running.  The 
tank  is  filled  with  water  up  to  the  brushes,  the  fruit  is  dumped  carefully 
into  the  portion  shown  in  the  foreground,  and  crowded  along  up  into 
the  circular  portion  where  it  enters  the  brushes,  is  carried  around 
between  them  and  then  lifted  by  revolving  arms  onto  the  grading  table, 
a  moving  belt  on  which  the  lemons  are  carried  past  the  graders  and 
distributed  by  them  according  to  color— dark  green,  light  green  or 
yellow— into  different  compartments.  This  machine,  in  various  modi- 
fications, is  in  almost  universal  use.  A  new  washer  gotten  up  by  the 
Limoneira  Company  has  a  square  wooden  tank,  brushes  in  the  form 
of  square  troughs,  and  the  grading  table,  all  in  a  straight  line.  (Fig.  2.) 
The  fruit  is  dumped  into  the  tank,  carried  up  by  revolving  arms  and 
belts  into  the  brushways,  rolled  and  carried  along  between  the  brushes 


6 


UNIVERSITY    OV   CALIFORNIA — EXPERIMENT   STATION 


by  moving-  brushes  which  form  the  bottom,  and  so  on  out  onto  the 
moving  belts  to  the  graders.     (Fig.  3.) 

The  severe  washing  and  scrubbing  to  which  much  of  the  fruit  1 


*■**" 

m   HP  w            f- 

1    r? 

i  it  iBr 

1 
1               Ik 

n 

/J 
•  II 

FIG   2.      Limoneira  washer.     Tank  end. 

be  subjected  in  certain  districts  is  a  very  undesirable  and  largely 
unnecessary  operation.  The  scale  and  smut,  to  remove  which  the  wash- 
ing   is   done,   may  be   very   completely   controlled   by  systematic    and 


Bulletin  190. 


BROWN    ROT    OF   THE    LEMON. 


thorough  fumigation,  and  the  necessity  of  severe  scrubbing  thereby 
eliminated.  The  latter  operation  is  expensive  and  can  not  fail  to 
injure  the  fruit.     The  ordinary  washing,  however,  even  where  nothing 


FIG.   3.     Grading  table  of  lemon  washer. 


more  than  an  almost  invisible  dust  is  removed,  is  decidedly  beneficial 
to  the  appearance  of  the  cured  fruit. 

As  it  comes  from  the  washer  the  fruit  is  placed  at  once  into  shipping 
boxes  while  still  wet,  and  is  then  put  away  for  curing. 


UNIVERSITY    OF   CALIFORNIA— EXPERIMENT   STATION. 


CURING  AND  STORING. 

The  methods  of  holding  lemons  for  curing  and  storing  have  been 
greatly  improved  in  recent  years.  This  is  largely  due  to  the  develop- 
ment of  the  Limoneira  system  of  tent-curing  in  open  houses.  The 
method  consists  in  storing  the  fruit  as  soon  as  washed,  usually  in 
shipping  boxes,  in  open-sided  sheds  exposed  to  the  freest  circulation  of 
air  and  outdoor  temperature.  The  boxes  of  fruit  are  stacked  in  square 
piles  of  about  a  carload  each,  each  lot  being  covered  with  a  canvas  tent, 
as  shown  in  figure  4.  These  tents  consist  of  canvas  tops  and  sides,  the 
latter  lacing  together  at  the  corners  and  rolling  up  on  the  sides.    Under 


FIG 


4.     Packing  lemons  for  shipment.      Shows  also  curing  tents. 
(Photo  by  L.   B.  Williams.) 


this  system  each  lot  of  fruit  can  be  given  its  proper  amount  of  ventila- 
tion, according  to  its  condition  and  that  of  the  atmosphere.  The  gen- 
eral object  aimed  at  is  to  gradually  dry  out  or  cure  the  fruit,  developing 
a  juicy  inside,  thin,  tough  rind,  yellow  color,  and  smooth  velvety  surface. 
Too  much  moisture  causes  softening  and  decay;  too  little  results  in 
wilting  and  withering  of  the  fruit  and  poor  curing  generally.  The 
"button"  or  stem  end  which  is  left  on  the  lemon  in  picking  is  the  best 
indicator  in  the  curing  process.  If  proper  conditions  are  maintained 
for  gradual,  uniform  curing  the  button  holds  tightly  to  the  fruit  and 
does  not  drop  off.  If,  on  the  other  hand,  the  fruit  is  weakened  by 
roper  treatment  the  buttons  begin  to  drop  off  and  separate  very 
easily   and    poor   keeping   quality   results.      Under   certain   conditions 


Bulletin  190.  BROWN  ROT  OF  THE  LEMON.  9 

shallow  trays,  like  those  seen  in  figure  4,  are  used  for  storage  instead  of 
boxes. 

In  the  drier  interior  regions  of  southern  California  the  tent  system 
is  not  as  satisfactory  as  nearer  the  coast,  on  account  of  too  rapid  drying 
of  the  fruit  in  summer,  even  with  the  tents  closed  continuously.  For 
this  reason  some  of  the  houses  in  that  section,  notably  the  Arlington 
Heights  Fruit  Company  of  Riverside  and  the  Corona  Lemon  Company 
of  Corona,  are  now  using  large  basement  rooms  to  a  considerable  extent 
for  curing  the  fruit.  These  are  arranged  for  ventilation  and  have 
various  features  adapted  to  their  peculiar  needs.  In  dry  summer 
weather,  even  near  the  coast,  it  is  usually  necessary  to  cover  the  top 
boxes  in  the  tent  with  papers  to  prevent  excessive  drying. 

The  condition  of  the  fruit  is  carefully  watched  during  curing,  and 
if  necessary  it  is  taken  down  and  sorted  during  the  process  to  remove 
decay.  This,  however,  should  not  ordinarily  be  necessary  except  on 
account  of  brown  rot,  a  phase  which  will  be  considered  later.  It  is 
desirable  to  handle  the  fruit  as  little  as  possible,  as  a  certain  amount  of 
bruising  and  consequent  decay  is  bound  to  result,  even  under  the  best 
conditions. 

When  fully  cured  the  fruit  is  either  shipped  at  once,  or,  if  in  good 
condition,  may  be  held  in  storage  in  the  tent  for  weeks  or  even  months, 
according  to  market  conditions. 

PACKING. 

When  ready  to  ship  the  fruit  is  sorted  from  the  storage  boxes  into 
trays  according  to  quality.  The  packer,  with  his  bench  for  the  box  and 
bunch  of  wrapping  paper,  then  wraps  each  lemon  in  tissue  paper  and 
packs  them  uniformly  in  the  boxes,  picking  out  the  particular  size 
which  he  is  packing  as  he  goes  along.  (Fig.  4.)  By  thus  selecting  the 
sizes  each  box  is  made  to  contain  a  certain  standard  number  of  lemons, 
and  is  thereafter  designated  by  the  number  and  quality  which  it  con- 
tains. The  pack  is  uniform  and  systematic,  the  packer  knowing  just 
how  many  lemons  he  will  put  into  the  box  and  arranging  them  accord- 
ingly, selecting  his  size  and  putting  a  certain  number  in  each  tier.  The 
packed  boxes  are  taken  to  the  nailer  (see  background,  Fig.  4),  who 
presses  the  cover  down  with  a  foot  power  press,  nails  it  at  the  ends,  and 
fastens  an  iron  strap  band  about  the  center. 

SHIPPING. 

In  forwarding  the  fruit  to  the  Eastern  markets,  lemons  are  shipped 
in  refrigerator  cars  in  order  to  control  the  ventilation  and  maintain 
uniform  temperature  and  moisture  conditions.  It  has  been  thoroughly 
demonstrated,  however,  that  with  fruit  properly  cured  and  handled 


10  UNIVERSITY    OF   CALIFORNIA—EXPERIMENT   STATION. 

the  use  of  ice  is  not  necessary  in  shipping  lemons,  and  a  number  of 
houses  are  shipping  the  year  round  without  it.  Not  only  is  the  expense 
of  icing  saved  (a  comparatively  small  matter  in  proportion  to  the 
value  of  the  shipment  were  icing  desirable),  but  the  fact  that  fruit 
will  carry  across  the  continent  without  ice  is  the  strongest  recommenda- 
tion of  its  future  keeping  quality  on  the  market.  On  the  other  hand, 
lemons  which  will  not  carry  without  ice  will  show  decay  sooner  or  later 
in  any  event.  Icing,  in  other  words,  does  not  prevent,  but  simply  post- 
pones or  temporarily  checks  decay.  The  individual  shipper  may  be 
able  to  sell  more  of  his  poorly  handled  fruit  by  this  means,  but  the 
whole  industry  is  bound  to  suffer  in  reputation  and  market  standing 
by  the  subsequent  decay  of  this  fruit  after  it  reaches  the  retailer  and 
consumer.  Shipping  successfully  without  ice  is  the  standard  which 
every  progressive  lemon-house  manager  will  set  for  himself  where  this 
is  not  already  accomplished. 

A  word  should  perhaps  be  added  in  favor  of  shipping  under  ice  on 
long  distance  shipments  in  hot  summer  weather,  in  order  to  preserve 
the  fresh,  unwilted  appearance  of  the  fruit.  This  is  not  a  matter  of 
decay,  but  simply  one  of  drying  and  shriveling,  where  the  fruit  may  be 
three  weeks  or  more  in  the  car  at  a  high  temperature.  Under  such  con- 
ditions the  use  of  ice  may  often  be  advisable  for  the  reasons  described, 
but  the  shipper  will  do  well  to  first  demonstrate  to  his  customers  his 
ability  to  ship  sound  fruit  under  any  conditions  without  the  use  of  ice, 
and  establish  what  is  by  far  the  most  valuable  asset  in  the  lemon  trade, 
a  firm  reputation  for  keeping  quality. 


THE  BROWN  ROT. 

Were  actual  conditions  which  have  obtained  in  the  past  few  years 
portrayed  in  the  above  account  of  lemon  handling,  it  would  be  necessary 
to  insert  in  almost  every  sentence  the  clause,  "Except  for  brown  rot." 
This  condition,  as  already  intimated,  has  come  to  affect  every  phase  and 
operation  of  the  business,  and  has  presented  a  very  serious  problem 
indeed  to  an  industry  already  with  its  full  share  of  complications. 

WHAT  BROWN  ROT  IS. 

Brown  rot  is  a  certain  form  of  decay  of  the  lemon  of  an  appearance 
and  nature  very  characteristic  to  one  familiar  with  it.  The  orange, 
pomelo  and  other  citrus  fruits  are  also  affected,  but  not  to  the  extent 
of  the  lemon,  on  account  of  the  methods  of  handling  the  latter  fruit. 
Brown  rot  in  the  packing  house  is  distinguished  most  clearly  by  two 
features:  its  rapid  spread  in  the  fruit  by  contact,  and  its  characteristic 
odor.    In  the  ordinary  blue  mould,  or  Penicillium  rot,  the  spread  of  the 


Bulletin  190. 


BROWN   ROT    OF   THE   LEMON. 


11 


decay  from  fruit  to  fruit  in  the  box  by  contact  is  not  common  or 
abundant.     Rather  the  condition  shown  in  figure  5  occurs.     Here  is 


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. 

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FIG.   5. 


Blue  mould,  or  Penicillium  rot,  in  box  of  lemons, 
without  infecting  others. 


One  lemon  affected 


seen  a  box  of  lemons  in  which  one  has  the  blue  mould,  but  this  has  com- 
pletely rotted  and  melted  down  without  infecting  any  of  its  neighbors, 


12  UNIVERSITY   OP   CALIFORNIA EXPERIMENT   STATION. 

though  the  latter  are  smeared  with  the  spores  of  the  fungus  and  the 
decayed  remains  of  the  lemon.  This  is  the  usual  condition  in  well- 
handled  fruit  in  respect  to  this  fungus.  A  lemon  here  and  there  which 
presumably  has  been  bruised  takes  the  Penicillium  rot,  but  no  spread  by 
eontact  occurs. 

Figure  6  shows  a  typical  condition  in  a  box  of  lemons  affected  by 
brown  rot.  Starting  with  one  lemon  the  decay  rapidly  spreads  to  those 
next  to  it.  from  these  to  the  next  and  so  on,  until  the  whole  box  is  gone. 
This  is  the  most  destructive  form  of  brown  rot,  because  of  the  fact  that 
a  single  affected  lemon  in  a  box  is  almost  certain  to  spread  the  rot  to 
the  whole  half-box  in  a  short  time.  The  decay  resulting  from  brown  rot 
is  a  very  filthy,  putrid  one.  It  is  characterized  further  by  the  pres- 
ence of  innumerable  small  flies  which  invariably  collect  in  swarms 
about  such  lemons,  and  breed  in  the  decaying  fruit.  The  maggots 
of  these  flies  contribute  very  largely  to  the  complete  decomposition 
which  takes  place  in  affected  lemons. 

The  odor  of  brown  rot  in  citrus  fruit  is  most  characteristic,  and  to 
one  familiar  with  it  serves  to  detect  even  a  very  small  amount  of  rot  in 
a  large  amount  of  fruit.  A  few  affected  lemons  will  betray  the  rot 
in  a  tent,  while  at  a  time  of  considerable  prevalence  the  whole  house 
smells  of  it.  This  odor  is  not  a  particularly  repugnant  one,  but  has  a 
characteristic  rancidity  and  penetration,  originating  presumably  in  a 
fatty  acid  produced  in  the  decomposition  of  the  oil  in  the  rind  of  the 
fruit.  The  little  flies  mentioned  above  seem  quick  to  detect  this  odor, 
and  the  first  cases  of  brown  rot  in  a  tent  of  fruit  are  sufficient  to 
attract  these  insects  in  a  manner  which  is  not  the  case  with  other  forms 
of  decay. 

Brown  rot,  then,  is  distinguished  from  blue-mould  rot  in  a  practical 
way  by  its  rapid  spread,  peculiar  odor  and  the  presence  of  numerous 
small  flies  on  the  boxes  containing  affected  fruit,  even  in  closed  tents. 
The  experienced  man  seeking  to  detect  the  rot  in  his  house  goes  through 
the  tents,  jarring  the  boxes  for  the  flies  and  sniffing  here  and  there  for 
the  odor.  By  these  means  he  will  detect  even  a  surprisingly  small 
amount  of  the  trouble. 

OCCURRENCE  OF   BROWN  ROT   IN   THE  ORCHARD. 

Little  has  been  said  as  yet  as  to  the  occurrence  of  this  trouble 
in  the  orchard.  It  is  common  there  in  affected  regions,  however, 
on  oranges,  pomelos,  tangerines,  etc.,  as  well  as  on  lemons.  It 
is  indeed  on  orchard-affected  fruit  that  we  see  the  trouble  more 
commonly  in  its  pure  condition,  unmixed  with  other  forms  of  decay. 
Our  colored  frontispiece  shows  typically  brown  rot-affected  lemons 
from  the  orchard.     Such  fruit  is  found  lying  on  the  ground  beneath 


Bulletin  190. 


BROWN   ROT   OF   THE   LEMON. 


13 


the  trees,  and  also  still  hanging  on  the  tree,  usually  within  two  feet  of 
the  ground,  but  occasionally  higher.     It  occurs  only  in  wet  weather 


PIG.   6.     Brown  rot  in  box  of  lemons.     Abundant  spread  by  contact. 

or  on  low  ground  after  irrigation,   always  more   abundantly   on   the 
lower,   heavier  soils  with  more  moisture,   and   has   become   extremely 


14 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT   STATION. 


abundant  in  most  of  our  lemon  orchards  .during  the  winter  and  spring 
season.  On  oranges  the  rot  is  commonly  seen  in  the  orchard  only  on 
fruit  lying  on  or  close  to  the  ground  in  very  wet  places.  The  rot  is  par- 
ticularly liable  to  occur  on  trees  standing  in  a  "wash."  in  the  orchard. 
where  drainage  water  runs  over  the  surface  and  keeps  the  ground 
beneath  the  trees  bare,  moist,  and  covered  with  sediment.  It  is  easily 
seen  that  a  considerable  amount  of  fruit  is  affected  while  still  on  the 
tree  and  then  falls  to  the  ground.  In  this  way  many  lemons  are  lost 
in  bad  cases,  as  in  figure  7,  where  the  fallen  brown  rot-affected  fruit 
ran  be  seen  on  the  ground.     Fully  a  box  of  fruit  to  the  tree  is  lost 


FIG. 


Brown   rot  in   the  orchard.      Fallen   lemons  affected  over   bare, 
uncultivated  ground. 


in  some  orchards  every  winter  in  this  way.  The  affected  fruit  is  not 
badly  decayed,  that  is,  it  is  not  softened  or  disintegrated  to  any  extent. 
The  rind  is  still  firm  and  the  tissue  sound.  No  appearance  of  mould  or 
fungus  is  seen  upon  the  surface.  There  is  simply  a  slight  discoloration, 
gradually  extending  from  a  center,  of  a  light  brownish  and  slightly 
purple  color,  not  extremely  prominent,  but  showing  light  on  dark  green 
fruit  and  dark  on  that  which  is  yellow.  Lemons  of  any  size  may  be 
found  affected  on  the  tree,  from  the  very  smallest  to  those  which  are 
mat ure.  The  decay  is  not  in  any  sense  one  of  old  or  weakened  fruit,  but 
affects  the  youngest  and  most  thrifty  to  an  equal  extent.  The  char- 
acteristic odor  is  distinguishable  from  the  very  first,  and  is  practically 
identical  in  the  different  citrus  fruits. 


Bulletin  190. 


BROWN   ROT    OF   THE   LEMON. 


15 


OCCURRENCE  OF  BROWN  ROT  IN  THE  PACKING  HOUSE. 

At  times  of  brown-rot  prevalence  there  is  always  more  or  less  orchard- 
affected  fruit  which  escapes  the  pickers  and  is  brought  into  the  house. 


P^  ,,■;.,.,'.. 

- 

%'  MM 

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m  W 

^nn 

FIG.    8.     Lemons  with  brown  rot  from  boxes  showing  white   growth  of  the 

Pythiucystis  fungus. 

This  has  the  same  appearance  as  that  seen  in  the  orchard  and  is  mostly 
thrown  out  at  the  washer  by  those  through  whose  hands  the  fruit  goes. 


FIG.  9.     Contact  infection  by  brown-rot  fungus. 

If  fruit  in  which  brown  rot  is  developing  be  examined  after  about  a 
week's  storage,  the  condition  shown  in  figure  8  will  be  found.    On  the 

2— bul.  190 


16 


UNIVERSITY    OF   CALIFORNIA EXPERIMENT   STATION. 


surface  of  affected  lemons  a  white,  delicate,  quite  abundant  mould 
develops,  and  it  is  natural  to  conclude  that  it  is  by  the  growth  of  this 
mould  that  the  contact  infection  and  spread  take  place.  Where  an 
affected  lemon  touches  another  the  growth  of  the  mould  from  fruit  to 
fruit,  as  in  figure  9,  is  evident,  and  in  advanced  cases,  like  figure  6.  the 
same  white  mould  can  be  seen  advancing  onto  new  fruit.  Affected 
fruit  iu  the  parking  house  soon  becomes  covered  with  the  blue-mould 
fungus,  which  obscures  any  other  characteristics,  but  when  new  the 
brown  rot  has  a  very  distinct  appearance  from  any  other  form  of  decay. 
The  worst  feature  of  the  rot  in  the  house  is  the  frequent  development 
of  the  trouble  in  great  abundance  in  fruit  which  showed  no  si^n  of  the 


ff:r  ^^^%^tK 

1  EiR      #  ' 

' 

FIG.   10.     Lemons  infected  with  brown  rot  by  soaking  in  infected  water. 

rot  when  washed  and  stored.  Granting  that  an  occasional  lemon  with 
orchard  infection  may  escape  the  men  at  the  washer  and  go  into  the 
tent,  it  is  still  a  fact  that  by  far  the  largest  amount  of  brown  rot  in 
the  tent  develops  in  fruit  which  was  perfectly  green  and  sound  when 
put  up.  Early  in  this  work  the  writer  has  carefully  watched,  for  hours 
at  a  time,  the  fruit  coming  from  the  washer,  finding  nothing  but  the 
finest,  dark  green  sound  lemons,  and  on  examining  the  same  fruit  later 
found  perhaps  several  affected  lemons  in  each  of  a  majority  of  the 
boxes  in  the  tent.  This,  with  the  rapid  spread  by  contact  which  begins 
jooii  as  the  rot  develops,  has  been  the  most  serious  and  discouraging 
feature  of  the  whole  situation. 

The  occurrence  of*  brown   rol   in  this  manner  begins  to  show,  under 


Bulletin  190.  BROWN  ROT  OF  THE  LEMON.  17 

average  conditions,  in  about  five  days  to  a  week  from  the  time  of 
washing  and  storing.  The  first  sign  of  the  rot  is  a  dark,  sunken  spot 
on  the  surface  of  the  lemon,  like  one  of  the  spots  shown  on  the  fruit 
in  figure  10.  Not  more  than  one  spot  on  a  lemon  is  commonly  seen  in 
ordinary  cases.  This  spot  rapidly  spreads,  a  discolored  area  develops 
on  the  lemon,  and,  if  there  is  moisture  enough,  the  white  mould  appears 
on  the  surface.  This  produces  the  stage  shown  in  figure  8,  or  that  of 
the  colored  frontispiece  if  there  is  not  moisture  enough  to  develop  the 
surface  mould.  Contact  infection  of  more  fruit  begins  at  once,  and  the 
conditions  shown  in  figures  8  and  6  result.  Lemons  infected  by  contact 
also  show  at  first  a  dark  colored  spot  at  the  point  of  infection.  At  the 
very  first  of  infection  of  this  sort  the  delicate  white  mould  can  be  seen 
attaching  itself  to  the  lemon,  growing  from  the  one  previously  affected, 
and  in  many  cases  this  can  be  wiped  off,  leaving  the  fruit  apparently 
intact.  In  the  majority  of  cases,  however,  and  practically  always  after 
the  dark  spot  has  appeared,  lemons  on  which  the  fungus  has  begun  to 
grow  develop  the  rot  and  can  not  be  saved. 


THE   CAUSE  OP   THE   BROWN   ROT. 

The  brown  rot  is  caused  by  a  fungus,  that  which  produces  the  white 
mould  seen  on  the  surface  of  affected  fruit,  as  in  figures  8  and  9.  This 
fungus  has  proved  to  be  a  hitherto  unknown  form,  and  has  been  named 
Pythiacystis  citrophthora*  It  is  an  active  parasite  of  citrus  fruit, 
readily  causing  infection  of  green  growing  fruit  by  means  of  its  spores 
or  by  growth  of  the  fungus  itself  from  one  fruit  to  another  when  in 
contact. 

DISCOVERY    AND    IDENTIFICATION    OF    THE    PYTHIACYSTIS    FUNGUS    AS    THE 

CAUSE   OP   BROWN    ROT. 

In  a  case  of  this  sort  it  is  not  sufficient  to  simply  find  a  fungus  of 
some  kind  growing  in  connection  Avith  affected  fruit,  in  order  to  posi- 
tively identify  the  cause  of  the  trouble.  For  the  strictest  proof  in  this 
respect  the  organism  must  first  be  found  to  occur  regularly  in  affected 
tissues;  it  must,  if  possible,  be  isolated  and  grown  in  pure  cultures, 
and  above  all  it  is  necessary  to  produce  the  typical  disease  artificially 
by  inoculating  healthy  material  with  the  suspected  organism  in  pure 
condition.  When  this  has  been  accomplished  we  are  safe  in  assuming 
that  we  have  found  the  cause  of  the  trouble.  In  the  case  of  the  brown 
rot,  where  the  cause  was  entirely  unknown  at  the  beginning  of  the 
investigation,  the  probability  was  quite  strong  that  the  white-mould 
fungus  which  appeared  on  the  fruit  was  the  cause  of  the  rot.     On 


♦Botanical  Gazette  42:215-221,  Sept.  1900. 


18 


IMVI'KSITY   OF   CALIFORNIA EXPERIMENT   STATION. 


lemons  free  from  other  fungi  it  could  plainly  be  seen  that  this  mould 
was  distinct   from  Penicillium,  and  the  occurrence  of  contact  infection 


E.H.S- 

FIG.    11.      Section  of  lemon   rind,   showing  brown-rot   fungus. 

like  that  shown  in  figure  9  left  little  doubt  that  this  fungus  was  the 
eause  of  the  spread  of  the  trouble.     Examined  with  the  microscope  it 


Bulletin  190.  BROWN  ROT  OF  THE  LEMON.  19 

was  found  that  the  tissue  of  affected  lemons,  even  when  no  mould  was 
visible  upon  the  surface,  was  full  of  the  filaments  of  a  fungus,  and  when 
kept  in  a  moist  chamber  the  typical  mould  at  once  developed  upon  the 
surface  of  such  fruit.     (Fig.  11.) 

Two  significant  facts  were  discovered  early  in  the  investigation. 
First,  that  if  affected  lemons  were  soaked  in  a  pail  of  water  for  a 
few  hours,  then  taken  out  and  good  fruit  put  in  for  a  similar  time, 
the  latter  would  invariably  become  badly  infected  with  the  typical  rot. 
(See  experiments  1-19,  1-24,  1-31,  1-51,  and  checks  in  many  others.) 
It  was  also  found  that  if  the  water  thus  infected  was  boiled  before  the 
good  lemons  were  put  in,  no  infection  resulted.  (Experiment  1-24.) 
This  was  satisfactory  evidence  that  some  living  organism  was  causing 
the  brown  rot.  Second,  it  was  found  that  if  affected  lemons  were  laid 
on  moist  soil  or  buried  just  beneath  the  surface,  the  same  white  mould 
soon  appeared  upon  the  soil.  Good  lemons  laid  on  the  same  ground 
soon  took  the  rot.  (Experiments  1-30,  1-33,  1-66,  1-83.)  All  then  that 
remained  was  to  grow  this  fungus  in  pure  cultures,  identify  it  and 
produce  the  rot  from  cultures.  This  has  been  accomplished.  After 
securing  a  pure  growth  of  the  fungus  in  culture  media  in  flasks,  it  was 
found  that  by  emptying  such  a  culture  into  the  pail  of  water  instead  of 
soaking  affected  lemons  in  it,  typical  brown  rot  resulted  in  lemons 
soaked  in  the  water.  (II-10a.)  This  completed  the  chain  of  evidence 
as  to  the  cause  of  the  trouble.  The  fungus,  after  much  technical  study, 
proved  to  be  a  form  not  previously  known  and  was  given  the  above 
scientific  name  and  described  in  the  journal  cited. 

NATURE  OF  THE  BROWN-ROT  FUNGUS. 

Pythiacystis  citrophthora  is  apparently  in  its  original  nature  a  harm- 
less and  inconspicuous  fungus  inhabiting  moist  soils  and  water.  But 
for  its  acquirement  of  this  remarkable  parasitism  of  the  lemon  it  might 
very  likely  have  never  been  discovered  or  attracted  any  more  attention 
than  many  other  microscopic,  unimportant  moulds  which  live  ,m  the 
soil. 

The  Fungus  on  the  Fruit. — As  it  occurs  in  the  form  of  the  white 
mould  seen  on  affected  lemons  and  causing  contact  infection,  the  most 
important  feature  of  the  fungus  is  the  fact  that  it  is  entirely  sterile, 
developing  no  spores  of  any  sort,  The  fungus  in  the  tissues  of  the 
lemon  and  on  the  surface  consists  simply  of  a  mass  of  filaments  of 
rapid,  vigorous  growth  when  supplied  with  moisture,  but  no  spores. 
This  is  a  most  important  fact.  In  a  case  like  that  of  the  blue-mould 
fungus  the  surface  of  affected  fruit  is  covered  with  a  fine  dust  which 
is  composed  of  inconceivable  numbers  of  the  spores  which  propagate 


20  UNIVERSITY    OF    CALIFORNIA EXPERIMENT   STATION. 

the  organism.  The  air,  the  dust,  every  box,  lemon  and  part  of  the 
packing  house  carries  an  abundance  of  these  spores  to  start  the  growth 
of  the  fungus  when  favorable  conditions  occur.  Were  this  so  with 
the  brown-rot  organism  the  case  would  indeed  be  serious,  since  the 
ability  of  the  latter  to  attack  sound  fruit  is  so  much  greater  than  that 
of  PenicUlium.  But  this  is  not  the  fact.  The  fungus  on  the  fruit 
develops  no  spores,  and  there  is  absolutely  no  more  infection  of  lemons 
after  they  leave  the  washer  except  by  contact.  The  fungus  simply 
grows  from  one  lemon  to  another,  starting  from  those  which  were 
already  infected  when  put  away,  and  no  new  lemons  become  infected 
except  in  this  way.  Many  affected  lemons  may  go  into  the  tent  in 
which  the  rot  has  not  developed  enough  to  show,  but  we  have  absolutely 
proven  that  the  fungus  produces  no  spores  in  the  packing  house  and 
does  not  have  the  slightest  means  of  spreading  there  except  by  vegeta- 
tive growth  from  lemon  to  lemon.  It  should  not,  however,  be  under- 
stood that,  even  by  the  closest  examination,  all  affected  lemons  can 
be  detected  as  they  come  from  the  orchard  or  washer.  One  of  the 
worst  features  of  the  whole  situation  has  been  the  abundant  rot  which 
often  starts  in  the  tent,  in  fruit  which  was  apparently  in  the  soundest, 
finest  possible  condition  when  put  away.  Such  occurrences  result 
from  infection  before  the  fruit  is  stored,  but  the  rot  does  not  develop 
enough  to  show  to  the  eye  for  several  days. 

Some  further  observations  are  to  be  noted  in  regard  to  this  fungus,  in  addition 
to  the  description  already  published.*  While  the  characteristics  there  given  have 
since  been  repeatedly  confirmed,  we  may  modify  one  clause  in  the  description  to 
the  following  extent.  The  original  reads,  "Aquatic  mycelium  typically  sterile,  with 
occasional  conidia  or  sporangia."  Sporangia  have  since  been  found  to  develop 
in  water  or  liquid  cultures  rather  profusely  in  many  instances  when  a  week  or 
two  old.  In  these  cases,  however,  the  zoospores  seldom  develop  normally,  the  proto- 
plasmic contents  usually  emptying  through  the  pore  without  division,  or  remaining 
within  the  sporangium. 

The  fungus  grown  on  moist  soil  never  fails  to  produce  normal  sporangia,  which, 
when  placed  upon  a  microscopic  slide,  rapidly  eject  their  swarmspores.  That 
spores  are  ejected  in  the  soil  is  evident  from  the  empty  sporangia  on  removal.  In 
soil  too  dry  to  produce  swarming  the  sporangia  retain  their  vitality  for  a  certain 
period  after  maturity,  but  after  remaining  in  this  condition  for  about  a  week  they 
fail  to  function,  even  after  prolonged  soaking. 

As  stated  in  the  former  paper,  dilute  prune  juice  appears  to  be  the  best  medium 
for  procuring  the  vegetative  stage  of  the  fungus,  in  which  it  develops  as  a  vigorous. 
profusely  branched,  continuous,  globular  mass  of  mycelium,  suspended  in  the  liquid, 
i  See  Fig.  1  in  paper  above  quoted.)  A  quick  and  sure  way  to  obtain  sporangia  is  to 
take  a  bit  of  mycelium  from  a  prune  culture  and  place  in  water  in  a  shallow  dish. 
Within  48  hours  the  fungus  fringes  out  at  the  edges  of  the  mass,  changing  from 
the  thick  vegetative  type  to  slender  threads  and  sporangiophores. 

Almost  limitless  variations  from  the  typical  shape  of  sporangia  are  to  be  found  in 
soil  and  water  cultures.  (Fig.  12.)  All  the  types  illustrated  have  been  found  in 
soil,  though  most  with  less  frequency  than  in  water.  Sporangia  with  two  or  three 
pores   I  Pig,   L2,  B,  C,  D)  are  common,  though  frequently  only  one  of  these  opens  for 


'See  Botanical  Gazette  42:215-221,  Sept.   1006. 


E.tt.S. 
FIG.  12.     Sporangiophores  and  sporangia  of  Pythiacystis,  showing  range  of  form. 


--  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION. 

the  passage  of  the  spores.  Intercalary  sporangia  are  rarely  found  (Fig.  12,  E  and  I) 
with  all  gradations  between  this  and  the  long-  water  sporangiophores  as  figured 
in  A.  figure  V2.  The  length  of  some  of  the  latter  is  extreme,  especially  when 
developed  from  affected  lemons  in  deep  water,  one  measured  being  over  1.6  mm. 
In  all  media  a  slight  swelling  at  the  base  of  the  sporangiophore  is  quite  character- 
istic, which  may  be  so  developed  as  to  present  the  appearance  of  a  series  of  nerve 
ganglia.  i  See  K.  Fig.  12  and  others.)  The  manner  in  which  the  sporangium 
joins  the  sporangiophore  varies  widely.  In  many  cases  the  sporangiophore  widens 
toward  the  junction,  which  we  at  first  took  to  be  characteristic.  (Fig.  15.)  In 
the  majority  of  later  cultures,  however,  the  sporangiophore  remains  of  uniform 
width  at  the  tip. 

In  rare  instances  the  sporangiophore  has  been  seen  to  grow  on  into  the  empty 
sporangium  from  the  point  of  insertion,  as  De  Bary  records  for  some  species  of 
Pyrhium   (Fig.  13.  K),  but  never  to  develop  further  than  as  figured. 

There  is  the  most  gradual  gradation  possible  here  between  De  Bary's  "conidia'- 
and  the  sporangia  with  zoospores.  (Fig.  13,  D- J. )  The  two  organs  are  apparently 
identical  in  development  up  to  a  point  where  ceriain  conditions  cause  them  in  the 
ease  of  conidia  to  germinate  from  the  pore  (which  is  always  formed),  while  other 
conditions  previously  described  bring  about  a  rounding  off  of  the  protoplasm  into 
zoospores.  A  conidium  on  germinating  will  sometimes  produce  a  true  sporangium 
within  a  few  microns  of  its  tip.  (Fig.  12,  F  and  L.)  Most  of  the  figures  of 
germinating  conidia  were  drawn  from  those  which  had  developed  on  an  affected 
lemon  floating  in  water.  It  is  under  these  conditions  that  the  conidia  develop  most 
freely,  the  sporangia  being  seldom  found.  In  pure  cultures  in  tap  or  distilled  water, 
if  at  all  fertile,  sporangia  are  more  commonly  developed  than  conidia.  most  of  the 
latter,  however,  being  imperfect  in  their  formation  of  swarmspores  as  before  stated. 

In  the  search  for  the  reproductive  organs  of  Pythiacystis  the  numerous  sprouts 
which  are  at  first  more  or  less  globular  have  been  rather  misleading.  (Fig.  13, 
A-C. )  Innumerable  variations  as  to  shape  are  found  among  these,  especially  in 
old  water  cultures.  From  old  seemingly  dead  mycelium  new  branches  will  push 
out  in  this  way  after  a  period  of  inaction,  without  a  change  of  medium,  though  the 
growth  in  this  case  is  spindling  and  not  long  maintained. 

As  yet  no  evidence  has  been  found  of  a  sexual  stage  in  the  life  history  of  the 
fungus.  Various  means  have  been  tried  in  the  attempt  to  develop  this  stage,  and  a 
careful  watch  kept  on  the  fungus  in  its  natural  environment.  We  have  satisfied 
ourselves  that  it  does  not  occur  as  an  economic  or  otherwise  important  factor,  or 
that  if  present  at  all  it  does  not  assist  the  fungus  to  live  through  periods  of  drought. 
It  is  interesting  to  note  in  this  connection  that  on  several  of  the  older  prune  cultures 
a  crusty  white  layer  developed,  one-eighth  inch  or  less  in  thickness,  with  very  much 
the  appearance  and  brittleness  of  lard  which  has  cooled  on  the  surface  of  a  liquid. 
At  first  this  was  thought  to  be  an  impurity,  but  a  layer  of  the  same  kind  has  since 
been  formed  on  cultures  known  to  be  pure.  The  formation  has  been  noted  to  some 
extent.  After  the  flask  becomes  filled  with  the  fungus,  which  then  comes  to  the 
surface  of  the  liquid,  a  thin  surface  scum  is  formed  which  grows  up  slightly  on  the 
sides  of  the  flask.  This  is  a  network  of  slender  mycelial  threads,  on  which  tight 
balls  of  mycelium  develop,  with  a  beginning  much  like  the  so-called  bud  formation. 
<  Fig.  13,  B.)  The  completed  layer  is  a  close,  sclerotium-like  mass  of  mycelium. 
We  shall  investigate  further  along  this  line. 

As  previously  stated,  this  fungus  grows  only  on  very  moist  media,  most  of  our 
work  being  done  with  liquid  or  wet  soil  cultures.     If  placed  on  a  solid  medium,  such 

agar-agar  or  potato  agar,  the  fungus  may  spread  through  the  medium  to  some 
at,  potato  agar  seeming  to  be  the  most  favorable  of  the  solid  media.  In  this 
the  organism   will  occasionally  produce  sporangia  of  a  degenerate  type. 

The  Modi  of  Sport  Formation  and  Infection. — It  was  particularly 
important  in  this  investigation  to  determine  accurately  the  manner  and 
place  in   which  the  primary  infection  of  the  fruit  takes  place.     Such 


E.H.S. 


FIG.  13.     Vegetative  bud  formation  and  conidia  of  Pythiacystis. 


24 


I-NIYKKSITY    OF   CALIFORNIA— EXPERIMENT   STATION. 


knowledge  must  underlie  any  logical  attempt  to  devise  means  for 
checking  the  occurrence  of  brown  rot.  Fortunately,  this  has  been 
accomplished,  and  the  results  of  the  investigation  in  this  direction  have 

proven  of  very  great  prac- 
tical value.  It  has  been 
found,  as  will  be  explained, 
that  there  are  two  modes  of 
infection,  in  the  orchard  and 
in  the  washer,  and  methods 
have  been  devised  by  which 
each  of  these  may  be  pre- 
vented, or  controlled  to  a  very 
large  extent. 

ORCHARD    INFECTION. 

The  fact  has  already  been 
mentioned  that  an  affected 
lemon  allowed  to  lie  on  the 
ground  soon  spreads  the 
fungus  to  the  soil  and  makes 
it  infectious  to  sound  fruit 
laid  upon  the  surface.  This 
demonstrates  that  the  fungus 
is  able  to  live  on  the  soil  and 
cause  infection  by  contact, 
just  as  it  grows  from  one 
lemon  to  another.  It  leads 
further  to  the  supposition 
that  the  soil  of  the  orchard 
must  be  a  breeding  place  of 
brown  rot,  on  account  of  the 
large  number  of  affected 
lemons  which  lie  and  decay 
on  the  ground  under  the 
trees. 

Further  than  this,  however, 

we  have  found  that  it  is  in 

the  soil  that  the  spores  of  the 

fungus     are    produced,     and 

that  this  is  the  original  source 

of  all  the  infection  of  lemons  except  that  wdiich  takes  place  by  contact. 

The  Pythiacystis  fungus  is  by  nature  a  soil  dweller.     Its  growth  on 

the  lemon  is,  in  a  sense,  an  abnormal  condition.    Its  spores,  as  in  other 

fungi   of  the  same  class,  are  produced  only  in  abundant  moisture,  a 


FIG.  14.  Brown-rot  fungus,  with  sporangia, 
in  wet  soil.  After  Smith  &  Smith,  Bot 
Gaz.,   loc.   cit. 


Bulletin  190. 


BROWN   ROT   OF   THE   LEMON. 


25 


condition  which  is  not  found  on  the  surface  of  a  lemon  in  air.  Laying 
an  affected  lemon  on  wet  soil,  or  on  moist  paper,  or  placing  a  mass  of 
the  fungus  from  a  culture  in  a  similar  situation,  we  soon  find  the  spore 
condition  developed  in  great  abundance.  This  is  of  the  rather  com- 
plicated type  known  as  sporangia  with  zoospores.  The  fungus  grows 
out  into  the  soil  producing  the  visible  mould  on  the  surface,  and 
amongst  this  are  found  numerous  rounded  bodies  of  microscopic  size, 
which    are   the   spores   or   sporangia.      (Fig.    14.)      Ordinary   fungus 


FIG.  15.  Showing  development  of  svvarmspores  from  sporangia  in  the  brown- 
rot  fungus.  In  the  sporangium  on  the  right  the  swimming  swarmspores  are 
escaping.     After  Smith  &  Smith,  Bot.   Gaz.,  loc.   sit. 

spores  are  simply  little  round  bodies  which  germinate  by  sending  out 
a  sprout  wherever  they  happen  to  be  lying,  if  moisture  and  other  favor- 
able conditions  are  present.  These  sporangia  of  fungi  of  this  type, 
however,  have  a  different  process.  They  develop  only  when  in  water. 
When  proper  conditions  come,  the  inside  of  each  one  divides  into  about 
thirty  smaller  spores  or  zoospores.  These  minute  bodies  are  of  a  nature 
more  animal  than  vegetable  in  their  appearance  and  action.  Each  is 
provided  with  two  fine,  hair-like  appendages  which  lash  vigorously 
about  in  water  and  enable  the  spore  to  swim  about  with  all  the  appear- 
ance and  activity  of  animal  life.  (Fig.  15.)  They  soon  come  to 
rest,  lose  their  power  of  movement,  and,  if  conditions  are  right,  each 


26  UNIVERSITY    OF  CALIFORNIA— EXPERIMENT   STATION. 

one  germinates,  sending  out  a  sprout  which  grows  into  a  filament  and 
produces  the  brown-rot  fungus  again.     (Fig.  16.) 

This.  then,  is  what  occurs  in  the  orchard.  Lemons  affected  with 
brown  rot  fall  to  the  ground.  The  fungus  grows  out  into  the  soil  and 
produces  its  mycelium  or  mould  growth,  which,  when  there  is  abundant 
moisture,  as  in  we1   weather,  develops  great  numbers  of  the  primary 


FIG.   16.     Germinating  swarmspores  about  six  hours  after  coming-  to  rest 

spores  or  sporangia  among  the  particles  of  the  soil.  These  lie  until 
they  become  decidedly  wet,  then  break  up  internally  into  a  large  number 
of  swimming  zoospores,  which  move  about  freely  in  Avhatever  moisture 
is  present,  finally  coming  to  rest  and  germinating  to  produce  the 
fungus  again. 

It  is  then  not  difficult  to  conceive  of  what  happens  in  regard  to 
infection  of  lemons  on  the  tree  with  brown  rot.  With  each  succeeding 
occ urrence  of  the  disease  the  soil  becomes  more  and  more  infested  with 
the  fungus.     In  wet  weather  and  particularly  in  low.  wet  ground,  the 


Bulletin  190. 


BROWN   ROT    OF   THE   LEMON. 


27 


organism  is  active  in  the  soil  and  develops  a  great  abundance  of 
sporangia.  These  lie  mixed  with  the  soil,  forming  a  part  of  the  finer 
surface  portion.     In  heavy  rain  they  spatter  up  with  the  dirt  onto  the 


FIG.    17. 


Experiment   in   preventing  brown    rot   by   covering   ground   under    tree 
with  burlap. 


lower  limbs  and  fruit  of  the  tree.  Zoospores  are  formed  in  the  moisture, 
occasionally  on  the  surface  of  lemons,  and  these  germinate  and  produce 
infection.  Thus  a  certain  amount  of  rot  occurs  on  the  tree  during  the 
wet  season,  and  on  account  of  the  nature  of  the  process  it  is  confined 
mostly  to  the  lower  portion  of  the  tree. 

It  is  very  easv  to  demonstrate  that  the  soil  under  the  trees  in  infected 


28  UNIVERSITY    OV  CALIFORNIA — EXPERIMENT   STATION. 

orchards  is  full  of  infection.  This  was  determined  in  our  investigation 
bv  soaking  good  lemons  in  water  containing  soil  from  such  places.  In 
the  brown-rot  season  a  small  amount  of  soil  taken  from  under  a  tree 
where  the  fruit  is  affected,  and  placed  in  a  bucket  of  water,  will  cause 
abundant  infection  of  almost  every  lemon  which  is  thereafter  soaked 
in  the  water.  Such  soil,  indeed,  has  been  found  to  be  the  most  favorable 
material  for  infection  and  disinfection  experiments,  producing  100% 
of  brown  rot  almost  invariably,  and  a  large  number  of  separate  infec- 
tions on  each  lemon,  as  in  figure  10.  (Experiments  1-83,  1-96,  and  all 
later  disinfection  experiments.) 

For  a  practical  demonstration  of  the  fact  that  infection  by  brown 
rot  does  come  from  the  ground  under  the  tree  in  the  manner  described, 
the  experiment  illustrated  in  figure  17  is  quite  convincing.  In  this 
case  four  representative  trees  in  an  orchard  badly  affected  with  the 
rot  were  chosen,  and  a  covering  of  burlap  stretched  under  each  tree  on 
a  wooden  frame  about  six  inches  from  the  ground.  This  was  in 
February,  when  the  rot  was  very  prevalent  on  all  the  trees  chosen  for 
the  experiment  and  much  of  the  bottom  fruit  had  already  been  lost.  A 
number  of  similar  trees  were  chosen  as  checks.  All  lemons  affected 
with  brown  rot  were  picked  from  all  the  trees  in  the  experiment  and 
from  the  ground  beneath  them.  Ten  days  later  all  the  affected  fruit 
was  again  removed,  in  order  to  get  all  that  had  been  infected  before 
the  experiment  started.  Had  the  experiment  been  begun  before  the 
large  amount  of  fruit  removed  in  these  two  pickings  had  become 
infected,  the  results  would  have  been  even  more  striking.  During  the 
period  from  February  8  to  April  15  two  brown-rot  lemons  developed 
on  each  of  two  of  the  burlaped  trees,  none  on  the  other  two.  In  each 
case  these  two  lemons  were  some  which  hung  low,  out  over  the  edge  of 
the  burlap,  and  were  not  protected  from  the  ground.  No  lemons  became 
affected  over  the  burlap,  and  none  at  all  on  the  other  two  trees.  Thirty- 
nine  check  trees  surrounding  the  others  (being  all  of  which  records  were 
kept)  showed  brown-rot  lemons,  respectively,  as  follows:  8,  11,  14.  10. 
14,  15.  12,  28,  19,  16,  19,  21,  21,  19,  9,  33,  10,  15,  12,  14,  24,  23,  17.  11, 
20,  26;  38,  17,  .4,  31,  26,  33,  31,  20,  27,  27,  33,  46,  53,  or  an  average  of  over 
20  per  tree.  It  should  also  be  noted  that  the  amount  of  brown  rot  on 
these  check  trees  was  decidedly  reduced  by  the  greater  or  less  covering 
of  the  soil  under  them  with  cover  crop  and  weeds.  In  every  case  those 
showing  a  comparatively  small  amount  of  rot  had  a  considerable  amount 
of  soil  covering,  which  had  an  effect  of  the  same  nature  as  that  of  the 
burlap  in  preventing  infection.  Trees  under  which  the  ground  was 
nearly  bare  fill  showed  from  30  to  50  brown  rots,  and  also  had  lost  very 
.ilv  l^-fore  the  experiment  began. 

This  experiment  substantiates  the  statement  that  orchard  infection 
with  brown  rot  comes  entirely  from  the  ground. 


Bulletin  190.  BROWN  ROT  OF  THE  LEMON.  29 

INFECTION  IN  THE  WASHER. 

It  has  already  been  stated  that  one  of  the  most  puzzling  features  of 
the  brown-rot  situation  has  been  the  great  prevalence  of  the  rot  in  the 
curing  tent,  in  fruit  which  when  put  up  seemed  perfectly  sound  and 
free  from  the  slightest  sign  of  decay.  It  is  admitted  that  some  orchard- 
infected  lemons  must  get  into  the  tents  when  the  trouble  is  abundant. 
This  could  hardly  be  otherwise,  when  lemons  in  all  stages  of  infection 
come  in,  with  the  affected  spots  not  particularly  conspicuous  and  some 
of  them  very  small.  A  great  deal  is  thrown  out  by  the  men  at  the 
washer,  but  naturally  some  escape  them.  Without  question,  too,  there 
are  times  at  which  a  large  amount  of  fruit  is  brought  from  badly 
infested  orchards  which  has  been  so  recently  infected  that  it  does  not 
show  the  presence  of  the  rot  to  the  eye  at  all.  This  fruit  looks  perfectly 
sound,  and  only  after  several  days  in  the  tent  does  the  fungus  develop 
enough  to  show  itself.     This  often  happens. 

But  a  common,  and  indeed  the  worst,  occurrence  of  brown  rot  can  not 
be  accounted  for  in  this  way.  At  times,  infection  and  spread  by  contact 
develop  in  the  tents  when  no  rot  whatever  is  showing  in  the  orchard, 
usually  in  early  summer  after  the  ordinary  brown-rot  season  is  over,  and 
in  amounts  out  of  all  proportion  to  the  apparent  orchard  occurrence, 
whatever  the  season.  This  has  proved  to  be  infection  from  the  washer, 
and  we  have  demonstrated  beyond  a  doubt  that  thousands  of  boxes  of 
sound  lemons  have  been  infected  with  brown  rot  in  the  washing  machine 
in  the  packing  houses,  that  the  rot  has  been  enormously  spread  in  this 
way,  and  that  in  this  lies  the  principal,  most  general,  and  most  easily 
prevented  source  of  infection  by  brown  rot. 

In  dumping  the  fruit  into  the  washer  tank,  box  and  all  are  submerged, 
if  possible,  in  order  to  float  the  lemons .  into  the  water  gently.  With 
them  go  leaves,  twigs,  blossoms,  the  dust  and  dirt  of  the  orchard  and 
considerable  soil  which  clings  to  the  bottom  of  the  boxes- where  they  have 
rested  on  the  ground.  At  the  end  of  a  day 's  run  there  is  a  large  amount 
of  sediment  of  this  sort  in  the  bottom  of  the  tank.  Knowing  the  nature 
and  habitat  of  the  fungus,  as  explained  above,  it  is. easy  to  see  how  the 
wash  tank  may  become  a  prolific  source  of  infection  of  sound  fruit  with 
brown  rot.  The  orchard  soil  and  dust  are  full  of  the  sporangia  of  the 
fungus.  When  dumped  into  the  washer  zoospores  are  produced  in  great 
abundance,  become  attached  to  the  lemons,  and  start  an  infection  which 
does  not  become  visible  until  several  days  later,  after  the  fruit  has  been 
stored.  One  of  the  chief  problems  early  in  the  investigation  was  to 
discover  how  the  wash  water  became  infected,  since  the  fact  that  it  was 
infectious  wTas  soon  discovered.  It  had  been  demonstrated  that  affected 
lemons  soaked  in  water  for  some  little  time  made  such  water  infectious, 
but  the  small  number  of  affected  lemons  which  get  into  the  washer  and 
the  short  time  that  they  stay  there  seemed  to  preclude  any  general 


UNIVERSITY    OF   CALIFORNIA — EXPERIMENT   STATION. 

infection  from  thai  source.  The  discovery  of  the  spore-producing  habit 
of  the  fungus  in  the  orchard  soil  first  revealed  the  real  manner  by  which 
the  spores  of  brown  rot  get  into  the  washer. 

Definite  experiments  have  proven  that  fruit  can  and  does  become 
infected  in  the  tank  in  this  way.  By  putting  a  shovelful  of  orchard 
soil  into  the  1,000-gaIlon  tank  of  a  washer,  and  then  running  lemons 
through  in  the  ordinary  way  for  washing,  it  was  found  that  from  10% 
to  40%  of  the  fruit  took  the  rot.  (As  to  the  infectiousness  of  the 
ordinary  wash  water,  see  experiments  1-12,  1-36,  II-3  and  11-16.  On 
the  infection  of  the  washer  with  soil,  see  IV-1,  IV-11,  IV-14  and  several 
following.     Also  Fig.  25.) 

Xot  only  does  the  fungus  become  introduced  from  the  orchard  into 
the  washer  in  the  manner  described,  keeping  the  water  continually 
infected,  but  experiments  have  shown  that  Pythiacystis  may  also  come 
to  inhabit  the  machine  permanently  if  not  destroyed  by  thorough  clean- 
ing or  disinfection.  It  has  seemed  in  many  cases  as  though  the  fungus 
was  being  bred  in  the  washer  itself,  rather  than  being  continually 
introduced  anew  with  each  day's  run.  This  condition  has  been  sug- 
gested especially  by  the  fact  that  the  rot  would  suddenly  and  completely 
stop  appearing  in  the  fruit  after  a  machine  had  been  very  thoroughly 
cleaned,  dried  out  for  some  time,  and  painted  inside.  Again,  fruit  of 
the  same  lot  would  rot  much  more  badly  when  washed  in  one  washer 
than  in  another.  To  test  this  we  have  experimented  by  soaking  various 
parts  of  the  machine  in  water  with  sound  lemons.  Besides  the  metal 
tank,  solid  frame  work  and  brushes,  these  washing  machines  contain 
various  pieces  of  cloth,  sheepskin  and  other  padding  to  protect  the 
fruit  from  bruising.  Soaking  this  padding  in  water  with  good  lemons. 
we  have  been  able  to  produce  brown  rot  in  considerably  large  amounts 
m  the  fruit.  This  therefore  indicates  that  the  fungus  is  able  to  grow 
and  propagate  in  the  machine  more  or  less,  attaching  itself  to  materials 
like  those  mentioned  above  which  are  favorable  for  its  development. 
The  brushes  also  become  quite  foul,  and  accumulate  large  amounts  of 
material  which  would  permit  the  growth  of  Pythiacystis.  The  whole 
operation  of  washing  lemons  under  ordinary  conditions  is  peculiarly 
favorable  to  infection  with  a  fungus  of  this  sort.  (See  experiment  1-41 
on  infection  from  washer  padding.) 

THE  CONTROL  OF  BROWN  ROT. 

To  the  practical  lemon  man  the  all-important  question  is.  How  shall 

prevent    or   control   this   trouble   in   an   economical   and   practical 

manner?     This  problem  we  have  attempted  to  solve  as  fully  as  that 

of  the  nature  and  habits  of  the  organism  causing  the  brown  rot,  but 

the  former  depends  upon  the  latter. 


Bulletin  190.  BROWN  ROT  OF  THE  LEMON.  31 

With  our  present  complete  knowledge  of  the  modes  of  infection  by 
brown  rot,  it  is  not  difficult  to  see  the  lines  along  which  we  must  proceed 
to  look  for  methods  of  completely  checking  the  trouble.  We  have  seen 
in  the  above  account  of  the  nature  of  the  rot  that  there  are  three  very 
distinct  sources  or  places  of  infection  of  lemons,  and  no  more.  These 
are :  in  the  orchard,  in  the  washer,  and  by  contact.  Upon  the  extent 
to  which  the  fruit  can  be  protected  from  infection  at  these  three  points 
depends  absolutely  the  extent  to  which  the  rot  may  be  eliminated  from 
our  lemons. 

CONTROL  IN  THE  ORCHARD. 

Since  the  infection  with  brown  rot,  or  the  spores  of  the  fungus  which 
produce  it,  originates  primarily  in  the  soil  of  the  orchard,  it  is  self- 
evident  that  if  we  could  exterminate  the  fungus  at  that  point  we  would 
succeed  in  checking  the  rot  absolutely  by  that  means  alone.  If  this  be 
not  practical  in  its  entirety,  it  is  at  least  possible  to  aid  very  materially 
in  eliminating  brown  rot  by  orchard  methods.  This  is  to  be  accom- 
plished, according  to  our  results,  by  two  general  methods:  first,  by 
checking  the  development  of  the  fungus  in  the  soil ;  second,  by  prevent- 
ing the  infection  of  the  fruit  on  the  tree  by  spores  from  the  ground,  by 
chemical,  cultural,  or  other  means.  In  •  connection  with  this  we  have 
made  considerable  study  of  the  life  and  distribution  of  the  fungus  in 
the  soil.  The  organism  is  doubtless  a  native  of  our  soils  in  wet  ground, 
but  might  not  be  expected  to  be  common  or  easily  found  under  ordinary 
circumstances.  We  have  never  succeeded  in  finding  it  in  any  soil  out- 
side of  citrus  orchards.  Our  method  of  soil  testing  for  this  fungus  has 
been  to  place  in  a  bucket  of  water  about  a  pint  of  the  soil  to  be  tested. 
Sound  lemons  were  then  soaked  in  the  water  for  various  lengths  of  time, 
then  put  away  in  a  box  in  a  curing  tent.  With  soil  where  the  fungus 
is  abundant  every  lemon  will  in  a  week's  time  show  very  numerous 
infections,  as  in  figure  10.  According  as  the  fungus  is  less  abundant 
less  infection  will  result.  A  very  small  amount  of  badly  infested  soil 
is  sufficient  to  produce  very  abundant  infection.  Pythiacystis  is  most 
abundant  in  the  soil  directly  under  the  trees,  where  the  fungus  is 
maintained  by  the  affected  fruit  which  falls  each  year  upon  the  soil. 
The  distribution  or  extent  of  the  occurrence  of  the  fungus  in  the  soil 
away  from  the  trees  is  governed  entirely  by  moisture  conditions,  and  in 
fact  its  whole  developmeift  depends  upon  a  large  amount  of  moisture, 
and  too  much  dryness  is  fatal  to  it.  In  the  wet  winter  season  soil  taken 
from  anywhere  in  the  orchard  in  affected  regions  is  highly  infectious 
and  full  of  the  fungus.  The  same  is  true  of  soil  which  washes  from 
the  orchard,  even  where  it  is  carried  for  considerable  distances.  In 
depth  the  soil  becomes  infested  for  at  least  4%  feet,  as  soil  down  to  that 
distance  has  been  found  to  infect  lemons.  (For  experiments  on  infec- 
3— bul.  190 


32  UNIVERSITY   OF  CALIFORNIA EXPERIMENT   STATION. 

tiousness  of  soil  from  different  depths,  locations,  etc.,  see  1-83,  1-96, 
IY-17.  IV-28,  IV-30,  IV-31,  IV-32,  V-6,  V-7.)  As  the  dry  summer 
comes  on  the  soil  away  from  or  between  the  trees  gradually  loses  its 
infectiousness,  and  after  it  has  thoroughly  dried  out  lemons  may  be 
soaked  in  water  with  any  amount  of  it  without  producing  brown  rot. 
Samples  of  the  most  infectious  soil  taken  in  winter  and  allowed  to  dry 
show  the  same  change.  A  soil  which  produces  100%  of  infection  and 
very  numerous  infections  on  every  lemon,  becomes  entirely  innocuous 
after  several  weeks'  drying.     (Experiments  1-80,  1-87.) 

In  the  orchard  the  activity  and  distribution  of  the  fungus  keep  on 
narrowing  and  lessening  with  conditions  of  increasing  dryness,  until,  in 
soils  which  are  not  kept  too  wet  by  irrigation,  the  organism  may  die 
out  altogether  on  the  surface.  Similarly  in  depth  the  fungus  recedes 
with  the  moisture,  leaving  the  upper  soil,  and  remaining  alive  only 
farther  down  where  there  is  more  dampness.  Near  ditches  and  flumes, 
where  the  ground  keeps  wet,  or  in  low  ground  where  irrigation  floods 
the  surface,  the  fungus  often  remains  active  all  summer  and  may 
produce  infection  of  fruit  on  the  trees  in  such  situations.  In  the  fall, 
when  rain  occurs  again,  Pythiacystis  again  begins  to  spread.  The  soil 
becomes  infectious  first  on' the  northwest  side  of  the  trees,  where  there 
are  most  shade  and  moisture.  Soil  from  this  location  always  produces 
infection  before  that  from  the  other  side  of  the  tree  or  that  between  the 
trees  has  any  effect.  The  rot  also  begins  to  show  first  on  fruit  on  the 
tree  at  this  point.  As  more  rains  occur  and  the  soil  becomes  saturated 
with  moisture,  more  and  more  rot  occurs  on  the  trees  on  all  sides, 'the 
affected  fruit  falls  to  the  ground  and  is  scattered  about,  rains  wash  the 
surface  soil  through  the  orchard,  the  fungus  grows  vigorously  in  the 
wet  ground,  and  soon  the  whole  body  of  soil  becomes  infested  and 
infectious  again. 

After  wTorking  out  quite  fully  these  features  in  the  life  history  of  our 
fungus,  with  the  results  described,  it  seemed  very  clear  that  in  orchard 
practice  anything  which  would  tend  to  stir  up  and  dry  out  the  surface 
soil  in  summer  would  be  of  practical  value  in  checking  brown  rot.  We 
therefore  have  urged  the  practice  of  thorough  summer  cultivation, 
especially  under  the  tree,  and  have  made  extensive  observations  as  to  the 
results  of  this  practice.  In  most  lemon  orchards  no  attempt  whatever 
is  made  to  cultivate  the  ground  beneath  the  trees.  The  plowing  and 
cultivation  go  up  and  down  and  across  the  rows,  working  the  soil  between 
the  rows  in  both  directions,  but  leaving  about  each  tree  a  square  of  soil 
which  receives  no  cultivation  whatever.  This  shows  quite  plainly  in 
figure  7.  Upon  this  soil  the  brown  rot-affected  lemons  drop  and  decay. 
With  them  are  the  leaves  and  rubbish,  accumulation  of  sediment  washed 
in  by  the  winter  rains,  lemons  decayed  by  other  causes  than  brown  rot, 


Bulletin  190.  BROWN  ROT  OF  THE  LEMON.  33 

and  all  the  various  refuse  materials  which  accumulate  in  such  a  place. 
Moisture  remains  here  near  the  surface  late  in  the  season  and  more  or 
less  all  summer.  The  soil  is  never  broken  up  or  aerated,  and,  in  short, 
presents  ideal  conditions  for  the  development  and  propagation  of  the 
brown-rot  fungus.  Theoretically,  to  thoroughly  break  up  the  soil  under 
the  tree  and  keep  it  cultivated  during  the  dry  season,  to  mix  up  the  old 
surface  layer  with  fresh  soil  and  let  it  dry  out,  and  to  clean  out  the 
accumulated  debris  and  decayed  matter  of  years  should  be  a  valuable 
means  of  keeping  down  the  brown  rot.  Practically,  the  growers  who  have 
done  this,  thoroughly  and  persistently,  have  obtained  excellent  results. 
This  does  not  mean  that,  in  orchards  where  brown  rot  is  abundant  and 
the  soil  under  the  trees  has  been  undisturbed  for  years,  a  single 
stirring  of  the  ground  will  stop  all  the  rot.  Neither  will  cultivation 
under  the  trees  during  the  wet  season  have  much  effect  on  the  develop- 
ment of  the  trouble  that  season,  as  some  have  seemed  to  expect.  The 
practice,  to  be  successful,  must  consist  in  a  thorough  and  rather  frequent 
breaking  up  and  stirring  of  the  soil  well  under  the  trees,  commencing 
in  spring  after  the  rains  cease  and  continuing  all  through  the  summer. 
If  this  is  accomplished  the  surface  soil  under  the  trees  is  pulverized  and 
dried  out  to  a  considerable  depth,  access  of  air  is  permitted,  and  the 
fungus  is  killed.  Instead  of  remaining  active  near  the  surface  all 
summer,  ready  to  start  into  more  active  growth  and  infect  all  the  lower 
fruit  on  the  tree  with  the  first  rains  or  even  a  heavy  irrigation,  the 
fungus  in  the  infested  soil  is  more  and  more  dried  out  with  each  culti- 
vation and  subjected  to  the  most  unfavorable  conditions  for  its  develop- 
ment. By  continuing  the  operation  all  summer  and  keeping  the  ground 
well  stirred,  brown  rot  the  next  winter  can  be  checked,  as  shown  by 
actual  experience,  to  a  very  decided  extent.  We  know  of  no  case  where 
the  practice  has  been  made  of  cultivating  under  the  trees  all  through 
the  summer,  where  the  amount  of  brown  rot  as  compared  with  neighbor- 
ing orchards  not  so  treated  has  not  been  very  markedly  reduced.  In 
certain  districts  some  of  the  very  best  and  very  worst  orchards  in  respect 
to  the  rot  are  situated  practically  adjoining  each  other,  and  the  only 
difference  to  which  the  absence  of  rot  in  the  former  can  be  ascribed  is 
the  fact  that  they  are  cultivated  under  the  trees  in  summer  while  the 
others  are  not.     (See  experiment  11-17,  A  and  B.) 

Methods  of  Cultivating  Under  the  Trees. — These  recommendations, 
we  are  aware,  are  somewhat  ill-adapted  to  the  style  of  pruning  most 
commonly  seen  in  many  of  our  best  lemon  orchards,  where  the  lower 
branches  are  allowed  to  spread  down  upon  the  ground  with  little  attempt 
at  cutting  out.  A  large  amount  of  fruit  is  produced  on  these  low 
branches,  where  it  can  be  easily  and  cheaply  picked,  and  we  would  not 
be  understood  as  unreservedly  condemning  this  style  of  tree.     The 


34 


UNIVERSITY   OF   CALIFORNIA — FXI'FRI.MFNT    STATION. 


grower  must  use  some  judgment  in  this  respect.  Our  strongest  point 
would  be,  however,  that  even  with  the  tree  very  close  to  the  ground  it 
is  possible  to  stir  up  the  soil  under  the  branches  much  more  thoroughly 
and  closer  to  the  trunk  than  is  commonly  done.  Even  if  the  lower 
limbs  are  dragged  and  the  lowest  fruit  scratched  a  little,  it  is  better 
to  carry  out  this  most  useful  method  of  checking  brown  rot,  rather  than 
to  lose  all  the  lower  fruit  wuth  the  rot  when  winter  comes,  and  allow 
the  fungus  to  flourish  unchecked  in  the  soil  to  be  carried  into  the  house. 
With  trees  like  those  shown  in  figure  18,  where  the  limbs  just  touch 
the  ground  without  lying  prostrate  upon  it,  it  is  an  easy  matter  to 


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FIG.    18.      Low-pruned  lemon  tree,  which   can   still  be   cultivated  under. 

cultivate  sufficiently  under  the  tree.  This  condition  may  be  maintained 
by  slight  pruning  at  the  bottom,  with  heavier  cutting  at  first  if  the 
limbs  are  low. 

One  of  the  most  efficient  means  of  cultivating  under  the  tree  known 
to  the  writer  is  a  spring-tooth  harrow  drawn  by  a  considerable  length 
of  chain.  After  the  ordinary  cultivation  of  the  orchard  between  the 
rows  in  both  directions,  a  team  is  attached  to  this  contrivance  and  the 
trees  are  "zig-zagged,"  the  team  going  to  the  right  of  the  first  tree  in 
the  row,  as  close  to  it  as  possible,  then  swinging  to  the  left  and  .going 
on  that  side  of  the  next  tree,  then  to  the  right  again,  and  so  on  down 
the  row,  coming  back  on  the  opposite  sides.  As  the  team  passes  around 
each  tree  the  harrow,  on  its  long  chain,  is  pulled  through  under  it. 
stirring  and  breaking  up  the  ground  in  the  corners  left  untouched  in 


Bulletin  190.  BROWN  ROT  OF  THE  LEMON.  35 

the  ordinary  cultivation.  This  can  be  clone  with  no  serious  damage 
with  trees  which  look  very  low  on  the  ground.  There  are  also  on  the 
market  several  cultivators  of  more  or  less  excellence,  made  for  the 
special  purpose  of  getting  under  the  trees.  In  many  cases  growers 
have  profitably  had  the  ground  under  the  trees  broken  up  by  hand, 
using  mattocks  or  hoes,  especially  in  cultivating  for  the  first  time 
ground  which  had  long  laid  undisturbed,  or  for  getting  farther  under 
than  could  be  done  with  a  team.  As  a  general  cultural  proposition, 
without  regard  to  brown  rot,  the  breaking  up  and  aeration  of  these 
dead,  decay  breeding,  uncultivated  areas  is  highly  desirable. 

For  destroying  the  rot  fungus,  the  more  the  ground  under  the  trees- 
can  be  stirred  during  the  summer  the  better.  The  work  should  begin 
in  spring,  before  the  ground  becomes  hardened,  and  an  effort  be  made 
all  through  the  summer  in  connection  with  the  usual  cultivation  to  stir 
and  work  the  ground  under  the  trees  and  get  it  thoroughly  dried  out 
and  stirred  as  deeply  and  as  often  as  possible.  The  theory  is  very 
simple:  Brown-rot  fungus  lives  over  summer  entirely  in  the  orchard 
soil.     It  is  killed  by  dryness.     Cultivation  produces  dryness. 

Chemical  Treatment  of  the  Soil.— After  discovering  the  soil  habit  of 
the  fungus,  and  the  fact  that  it  is  carried  over  the  summer  entirely 
in  the  ground  under  the  trees,  the  idea  presented  itself  that  it  might  be 
feasible  to  kill  the  rot-producing  organism  in  the  soil  by  applying  some 
fungicidal  substance  or  liquid.  The  possibilities  in  this  direction  have 
been  tried  out  quite  thoroughly,  but  with  no  very  promising  results. 
While  it  is  entirely  feasible  to  kill  the  fungus  in  this  manner,  the 
amount  of  liquid  required  to  saturate  the  soil  to  a  depth  sufficient  to 
be  of  any  value,  or  the  amount  of  any  dry  substance  necessary  to  cover 
the  surface  heavily  enough  to  keep  down  the  fungus,  is  so  great  that 
the  expense  and  labor  involved  prohibit  the  use  of  methods  of  this  sort. 
Figuring  the  depth  and  area  of  soil  necessary  to  be  treated,  the  cost 
of  material  which  would  be  required  in  an  orchard  of  any  size,  with  the 
labor  of  applying  it,  would  amount  to  more  than  the  value  of  the  fruit. 
The  experiments  along  this  line  were  made  principally  with  copper 
sulphate,  formalin,  lime  and  sulphur. 

Experiments  with  Copper  Sulphate.— U sing  small  boxes  of  soil  in 
which  brown  rot-affected  lemons  had  been  mixed,  it  was  found  that 
good  lemons  laid  on  the  surface  soon  became  affected  with  the  typical 
decay.  When  boxes  of  soil  thus  prepared  were  saturated  with  a  strong 
solution  of  copper  sulphate,  the  fungus  and  the  power  of  infection 
appeared  to  be  completely  destroyed.  Good  lemons  laid  on  such  treated 
soil  remained  sound  indefinitely,  if  not  destroyed  by  other  forms  of 
decay.     The  solution  used  in  these  experiments  contained  3%  copper 


UNIVERSITY    OF   CALIFORNIA — EXPERIMENT   STATION. 

sulphate  and  was  applied  in  sufficient  quantity  to  thoroughly  saturate 
the  soil.  This  strength  is  far  above  what  could  be  used  in  a  practical 
way  in  the  orchard,  both  on  account  of  the  expense  and  the  injurious 
effect  on  the  soil.  Experiments  with  the  use  of  1-10,  1-12,  1-100  and 
1-200%  copper  sulphate  showed  little  or  no  retardation  of  the  rot. 
See  experiments  1-30,  1-65,  1-66.)  In  experiments  on  orchard  soil  it 
was  found  that  very  large  amourits  of  water  were  required  to  saturate 
even  an  inch  or  two  of  the  surface.  On  rather  dry  ground  500  gallons 
per  tree  was  not  sufficient  to  give  results  of  any  promise  in  regard  to 
thorough  saturation.  Furthermore,  it  was  found  that  the  neutralizing 
•effect  of  the  soil  upon  the  sulphate  solution  was  such  as  to  make  the 
minimum  strength  required  to  kill  the  fungus  much  greater  than  that 
found  effective  when  the  organism  or  its  spores  were  in  water.  It  is 
in  fact  practically  impossible  to  sterilize  the  soil  to  any  depth  by  this 
means,  except  by  the  use  of  enormous  quantities  of  material.  We  have 
therefore  given  up  all  thought  of  the  use  of  this  method.  (See  experi- 
ment 1-90.) 

Experiments  with  Formalin.— The  strength  of  this  disinfectant  is 
not  neutralized  by  the  soil  to  the  extent  that  copper  sulphate  is  thus 
affected.  With  small  amounts  of  soil,  as  in  boxes,  it  is  possible  to 
completely  exterminate  the  brown-rot  fungus,  but  in  orchard  practice 
this  is  out  of  the  question. 

Experiments  with  Lime. — It  was  found  that  a  heavy  covering  of  air- 
slaked  lime  has  a  decided  influence  in  checking  the  rot  fungus  in 
affected  soil.  To  have  the  desired  effect,  however,  it  is  necessary  to  put 
on  a  solid  covering  an  inch  or  more  in  depth  all  over  the  surface,  and 
keep  this  undisturbed.  No  way  has  appeared  of  doing  this  economically 
and  practically.  The  effect  on  the  soil  of  the  amounts  of  lime  which 
would  soon  accumulate  from  the  continued  applications  necessary  is 
also  an  objection  to  this  treatment. 

Experiments  with  Sulphur. — A  coating  of  sulphur  on  the  soil  has 
shown  some  effect  in  keeping  down  the  fungus  in  box  experiments,  but 
nothing  of  value  for  actual  practice. 

From  the  results  of  these  various  experiments  in  soil  treatment  it 
will  be  seen  that  the  only  apparently  practical  method  of  checking  the 
rot  by  such  means  lies  in  thorough  summer  cultivation  of  the  ground 
under  the  trees.  We  lay  particular  stress  on  this  matter  because  it 
represents  a  rational  method  of  ordinary  cultural  practice  and  a  desir- 
able improvement  in  the  present  practice  in  many  orchards,  as  well  as 
a  means  of  overcoming  the  brown  rot  to  a  very  marked  extent.  In  our 
mind  it  is  the  highest  achievement  in  plant  pathology  to  demonstrate 


Bulletin  190.  brown  ROT  OF  THE  LEMON.  37 

methods  which  in  themselves  represent  improved  practice  from  the 
cultural  standpoint,  whereby  definite  pathological  difficulties  may  at 
the  same  time  be  overcome.  The  results  attained  where  this  method 
has  been  properly  carried  out  have  been  so  satisfactory  that  we  have  not 
thought  it  necessary  or  advisable  to  go  further  with  investigations 
having  in  view  the  saturation  of  the  soil  with  substances  injurious  to 
plant  life,  even  though  superficially  the  latter  may  show  results  of  value. 


THE  PREVENTION  OF  INFECTION  IN  THE  ORCHARD. 

We  have  previously  stated  that  brown  rot  may  be  controlled  in  the 
orchard  either  by  eliminating  the  fungus  from  the  soil  or  by  protecting 
the  fruit  from  infection,  and  have  discussed  the  chemical  and  cultural 
means  of  attaining  the  former  end.  While  it  is  true  that  the  practice 
of  cultivation  under  the  trees  in  summer  has  succeeded  in  entirely 
eliminating  the  rot  in  a  number  of  cases,  and  always  shown  most  satis- 
factory results,  yet  in  connection  with  this  method,  or  where  it  has  not 
been,  or  for  any  reason  can  not  be  carried  out,  it  is  very  desirable  to 
find  every  other  possible  way  of  preventing  infection  of  the  fruit. 
Even  though  the  fungus  be  present  in  the  soil,  it  is  possible  to  largely 
reduce  the  infection  which  ordinarily  takes  place. 

Pruning  Up  the  Trees. 

An  effective,  though  not  entirely  practical  means  of  controlling  brown 
rot,  is  found  in  pruning  up  the  trees  so  that  none  of  the  fruit  hangs 
within  two  or  three  feet  of  the  ground.  (See  Fig.  19.)  We  have 
experimented  somewhat  along  this  line  and  found  that  in  the  worst 
infected  orchards  trees  pruned  up  to  the  latter  height  showed  no  more 
rot.  This  simply  amounts,  of  course,  to  cutting  off  the  lower  fruit 
instead  of  leaving  it  to  become  infected.  There  is  a  practical  benefit, 
however,  in  greatly  lessening  the  amount  of  infected  fruit  which  is 
carried  into  the  washer  and  tents.  It  therefore  will  pay,  to  a  moderate 
extent  at  least,  to  prune  up  the  trees  and  get  the  fruit  up  off  the 
ground.  In  low,  heavy  ground,  where  it  is  difficult  to  prevent  surface 
flooding  around  the  trees  in  irrigation  and  where  the  water  from  the 
rains  settles  and  stands,  we  believe  it  will  pay  the  grower  to  adopt  a 
taller,  higher  style  of  tree  and  keep  the  fruit  up  at  least  two  feet  from 
the  ground.  This  will  save  an  immense  amount  of  trouble  from  such 
places  in  wet  weather. 

Considerations  of  pruning  and  cultivation  under  the  tree  naturally 
go  together.  In  cases  of  bad  rot  in  the  orchard  we  recommend  radical 
treatment  in  both  directions,  trimming  the  trees  up  quite  severely  and 
stirring  the  ground  under  them  in  summer  very  thoroughly  and  fre- 


38 


UNIVERSITY   OF  CALIFORNIA — EXPERIMENT   STATION. 


FIG.   19.     Lemon  trees  pruned  high. 

quently.  The  limbs  may  then  be  allowed  to  gradually  come  down  again 
until  the  condition  is  reached  which  seems  to  be  the  most  desirable 
under  the  circumstances.  As  said  above,  a  large  amount  of  cheaply 
handled  fruit  is  produced  near  the  ground ;  the  grower  must  decide, 
according  to  the  extent  of  his  trouble  with  rot  or  his  success  in  handling 
it  by  other  means,  what  policy  he  shall  adopt  as  to  pruning. 


The  Use  of  Cover  Crops  as  a  Means  of  Preventing  Orchard  Infection. 

One  of  the  earliest  orchard  observations  made  in  connection  with 
this  work  was  the  fact  that  on  trees  under  which  the  ground  was 
covered  with  a  green  growth  in  winter  there  was  much  less  rot  than 
over  bare  ground.  Carried  further,  and  observed  more  carefully,  it 
was  found  that  on  the  same  tree  the  fruit  on  a  limb  hanging  over  bare 
ground  would  rot  badly,  while  that  over  a  clump  of  weeds  or  other 
growth  remained  unaffected.  When  fully  appreciated  and  looked  for 
particularly,  in  lemon  orchards  in  all  the  different  sections,  the  impor- 
tance of  this  discovery  became  evident.  It  was  thought  at  first, 
theoretically,  that  weeds  or  cover  crops  under  the  trees  in  winter  would 
favor  the  rot  by  holding  moisture.  Practically  this  is  not  the  case,  but 
just  the  opposite  is  true.  Invariably  where  there  is  much  growth  on 
the  ground  the  rot  occurs  on  limbs  hanging  over  bare  ground,  and  only 
to  a  very  limited  extent  over  the  covered  ground.  With  a  knowledge 
of   the   nature   of   the   fungus,    the   fact   thus   established   is   readily 


Bulletin  190. 


BROWN   ROT   OF  THE  LEMON. 


39 


ft '                      Jfy 

.  V"-    ' 

'■■"■■' 

•v>;\  '  .4    ,.   -^    ,:'] 

■ 

'""■'    '■'"» ' ■ : ; — ; — — — sati. 

FIG. 


20.     Sound  lemons  hanging  over  cover-crop  of  vetch.     The  previous  winter  this 
same  tree  with  the  ground  bare  was  badly  affected. 


explained.  It  is  simply  that  the  growth  covers  the  ground  and  prevents 
the  dust  and  dirt,  with  the  spores  of  the  fungus,  from  getting  on  the 
fruit.  The  experiment  of  tenting  under  the  trees  with  burlap,  shown 
in  figure  17,  was  devised  with  the  demonstration  of  this  particular  point 
in  mind.  By  this  means,  as  already  described,  infection  was  entirely 
checked,  and  the  fact  demonstrated  that  orchard  infection  takes  place 
by  spores  coming  from  the  ground  under  the  tree. 

It  is  not  probable  that  any  grower  will  see  his  way  clear  to  cover  the 
ground  under  his  lemon  trees  with  burlap  or  other  similar  material, 
though,  if  he  could  do  this,  it  would  be  with  the  absolute  assurance 
that  all  orchard  infection  with  brown  rot  would  be  prevented,  no 
matter  how  badly  the  soil  was  infested.  The  fact  is  a  positive  one, 
that  any  covering  between  the  soil  and  the  lower  limbs  of  the  tree 
prevents  brown-rot  infection  to  the  extent  that  it  actually  covers  the 
ground.  The  whole  area  of  the  orchard  does  not  need  to  be  covered, 
as  infection  apparently  takes  place  only  from  the  soil  directly  under  a 
lemon  by  dirt  spattering  up  with  the  rain,  except  in  the  case  of  large, 
thick  trees,  which  retain  a  large  amount  of  moisture. 

After  observing  the  effect  of  weeds  on  the  ground  in  keeping  down 
the  rot,  the  most  natural  thought  was  of  cover  crops,  another  oppor- 


40  UNIVERSITY   OF  CALIFORNIA EXPERIMENT   STATION. 

tunity  of  making  good  cultural  practice  do  double  duty.  If  a  chance 
growth  of  weeds  would  show  such  decided  effects,  it  seemed  reasonable 
that  much  more  would  be  gained  from  a  regular,  sowed  crop.  With 
this  in  mind  growers  have  been  urged  to  sow  cover  crops  in  their  lemon 
orchards,  especially  under  the  trees,  and  the  results  have  been  entirely 
in  accord  with  the  earlier  observations.  These  crops  have  naturally 
been  more  or  less  successful,  both  as  cover  crops  and  as  rot  preventives, 
and  the  fact  has  been  very  plainly  established  that  such  a  covering 
will  prevent  infection  in  proportion  to  the  amount  of  growth  which  the 
crop  makes  under  the  trees  during  the  season  when  the  rot  is  active. 
A  heavy,  solid  growth  early  in  winter,  under  trees  which  had  formerly 
lost  all  the  bottom  fruit,  has  almost  entirely  eliminated  the  trouble, 
lemons  close  to  the  ground  remaining  unaffected  where  over  bare 
ground  they  would  never  reach  half  size.     (See  Fig.  20.) 

As  to  the  kind  of  crop  to  be  used,  the  time  of  sowing,  method  of 
handling,  etc.,  we  would  simply  say  that  the  only  consideration  so  far 
as  brown  rot  is  concerned  is  to  get  a  good  heavy  growth  all  over  the 
ground,  under  the  trees,  early  in  winter.  To  accomplish  this,  the  crop 
must  be  planted  early,  in  September  or  October,  and  irrigated,  if 
necessary,  to  produce  a  rapid  growth.  Under  the  trees  the  seed  must 
be  sown  by  hand,  and  may  have  to  be  raked  in  to  some  extent.  As  to 
the  crop  to  be  sown,  there  is  some  latitude  of  choice,  and  no  one  plant 
can  be  named  as  preeminently  the  best  under  all  conditions.  Of  the 
leguminous  plants  in  common  use  as  cover  crops  the  vetch,  Canada  pea, 
fenugreek  and  native  bur-clover  have  been  used  in  our  experiments 
and  observed  in  many  orchards.  The  pea,  used  alone,  is  rather  too 
coarse  and  spreading  a  plant  to  cover  the  ground  as  completely  and 
quickly  as  is  desirable,  and  does  not  grow  as  w^ell  in  the  shade  as  some 
of  the  other  plants.  It  may  be  used  mixed  with  other  seed  to  thicken 
and  support  the  growth.  Fenugreek  grows  poorly  in  the  shade  and  is 
easily  set  back  by  dryness,  so  that  it  does  not  seem  desirable  for  this 
purpose.  Bur-clover  is  somewhat  capricious  in  its  nature,  requiring 
an  early  start  and  plenty  of  water  to  cover  the  ground  as  early  in  the 
season  as  is  necessary  to  keep  down  brown  rot.  It  grows  well  in  the 
shade  under  the  trees.  Vetch  has  the  same  requirements,  but  does  very 
well  under  the  tree  and  when  well  grown  makes  an  ideal  ground  cover- 
ing. If  started  not  later  than  October  and  given  water  enough  (which 
must  be  done  with  any  crop  to  get  a  thick  growth);  this  may  be  regarded 
as  the  best  plant  for  our  purpose.  In  most  of  our  lemon  sections  there 
is  already  sufficient  information  on  hand  to  indicate  what  crop  will 
best  answer  the  requirements  for  that  particular  region.  To  cover  the 
ground  completely,  well  under  the  trees,  and  early  in  winter  before  the 
rainy,  brown -rot  season  is  too  far  advanced,  is  the  only  object  which  is 
of  any  value  to  this  method. 


FIG.     21.       Ideal    summer    condition    of    lemon    orchard    for    brown-rot    control. 
Lower  branches  just  touching  the  ground,  and  soil  beneath  well  cultivated. 


FIG.  22.     Ideal  winter  condition  of  lemon  orchard  for  brown-rot  control.     Heavy 
crop  of  vetch  under  the  trees.     Trees  need  not  be  pruned  so  high. 


42  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION. 

Ill  brief,  then,  we  recommend  as  one  of  our  major  conclusions  in 
brown-rot  control,  the  sowing  of  a  cover  crop  in  lemon  orchards  in  the 
fall,  planting  the  crop  for  this  purpose  especially  under  the  trees. 
Naturally  the  crop  will  also  be  planted  all  over  the  ground  for  the 
ordinary  purposes  of  a  cover  crop.  The  plant  to  be  used  must  be  one 
which  makes  a  good  winter  growth  and  a  thick,  dense  covering  on  the 
ground  in  as  short  a  time  as  possible,  particularly  in  the  shade  under 
the  trees.  Vetch  and  bur-clover  seem  to  be  among  the  best  plants  for 
this  purpose,  especially  the  former.  For  good  results  the  crop  should 
be  planted  in  September  or  early  October,  sowing  by  hand  under  the 
trees,  and  the  ground  then  furrowed  out  so  that  it  can  subsequently  be 
irrigated.  If  fall  rains  are  lacking,  the  ground  should  be  irrigated 
and  the  cover  crop  pushed  along  as  fast  as  possible.  If  this  is  done,  a 
good  ground  covering  can  be  obtained  by  the  time  that  the  rot  begins 
to  be  abundant  in  January.  If  possible,  the  crop  should  be  left  on  the 
ground  until  the  rainy  season  is  nearly  over.  After  plowing-in  the  crop 
summer  cultivation  should  begin  as  already  described.  Figures  21 
and  22  show  the  ideal  summer  and  winter  condition  of  a  lemon  orchard 
for  controlling  brown  rot. 

We  have  considered  only  the  leguminous  crops,  owing  to  their  value 
as  soil  enrichers,  as  well  as  the  benefit  to  be  derived  from  them  in 
suppressing  brown  rot.  There  are  cases,  however,  where  a  sowing  of 
barley  or  any  quick-growing,  vigorous  crop  is  of  great  value  in  control- 
ling brown  rot  in  the  orchard.  The  worst  cases  of  rot  are  usually  in 
places  where  there  is  a  wash  through  the  orchard,  the  ground  being 
kept  bare  and  moist  by  surface  water  running  down  from  farther  up 
the  slope.  There  are  also  cases  where,  for  one  reason  or  another,  it  is 
impossible  to  get  a  leguminous  cover  crop  started  and  properly  grown 
in  time  to  keep  down  the  rot.  In  such  cases  a  sowing  of  barley  will 
often  be  most  useful.  By  this  means  a  quick  growth  is  obtained,  which 
prevents  the  water  washing  over  the  surface  to  quite  an  extent,  keeps 
the  ground  covered  under  the  trees,  and  aids  very  materially  in  pre- 
venting infection  by  brown  rot.  In  badly  affected  orchards  the  first 
aim  of  the  grower  should  be  to  prevent  any  washing  of  water  over  the 
surface,  and  to  get  a  green  covering  of  some  kind  on  the  ground,  espe- 
cially under  the  trees,  before  the  heavy  rains  come  on.  The  bare  slopes, 
where  the  water  of  every  storm  washes  over  the  surface  unrestricted, 
and  the  low,  wet  ground  where  water  accumulates  and  stands,  are  the 
principal  breeding  places  of  brown  rot  in  the  orchard. 

Tin:  Use  of  Artificial  Coverings  o.\   the  Ground  for  Preventing 
Brown  Rot  Infection. 

The  decided  success  obtained  by  covering  the  ground  with  green 
crops,  and  by  the  burlap  method,  suggested  the  possibility  of  spread- 


Bulletin  190. 


BROWN   ROT   OP   THE   LEMON. 


43 


ing  some  other  substance  under  the  trees  to  protect  the  fruit  from 
infection.  It  is  undoubtedly  true  that  a  layer  of  any  substance  which 
would  cover  the  ground  thoroughly  would  answer  the  purpose  and 
keep  down  rot  effectively,  the  only  question  being  that  of  economy. 
The  only  substance  which  has  suggested  itself  as  being  at  all  cheap 
and  abundant  enough  for  this  purpose  is  straw.  This  in  some  cases 
can  be  obtained  cheaply  enough  to  make  feasible  a  heavy  covering  under 
each  tree  in  the  orchard.  Figure  23  shows  an  experiment  of  this 
nature.  Four  trees  were  chosen  where  rot  had  been  abundant,  and 
all  affected  fruit  removed,  as  with  the  burlap  trees.    The  ground  under 


FIG.   23.     Control  of  brown  rot  by  covering  ground  under  tree  with  straw. 

each  tree  was  thoroughly  covered  with  straw,  using  about  a  bale  to  the 
tree.  During  the  remainder  of  the  winter  only  two  lemons  became 
affected  with  brown  rot  on  the  straw-protected  trees,  and  these  were 
on  limbs  which  hung  out  over  bare  ground.  The  record  of  the  30 
unprotected  check  trees  is  given  on  page  28,  in  connection  with  the 
burlap  experiment,  showing  from  4  to  53  brown-rot  lemons  per  tree, 
with  an  average  of  over  20.  There  is  no  question  that  this  is  a  most 
effective  measure,  and  in  bad  cases  of  orchard  infection,  where  the 
straw  can  be  obtained  at  any  practical  figure,  we  strongly  recommend 
its  use  in  the  winter  season,  both  in  connection  with  summer  cultivation, 
and,  if  possible,  with  the  cover-crop  method.     The  amount  of  straw 


44  UNIVERSITY   OF  CALIFORNIA — EXPERIMENT   STATION. 

available  is  the  only  limitation.     If  the  ground  can  be  solidly  covered, 
brown-rot  infection  can  be  absolutely  prevented. 

There  <are  possibly  other  substances  which  will  suggest  themselves 
for  this  purpose,  which  can  be  obtained  in  individual  cases.  Anything 
which  will  cover  the  ground  in  the  manner  described,  without  injurious 
effects  of  any  sort  to  the  tree  or  soil,  will  prove  effective. 

THE    CONTROL   OF   BROWN   ROT    IN   THE   PACKING   HOUSE. 

The  more  striking  results  of  this  work  have  been  obtained  in  the 
treatment  of  lemons  for  the  prevention  of  brown  rot  in  the  packing 
house,  regardless  of  conditions  in  the  orchard.  This  is  the  case,  how- 
ever, simply  because  with  the  picked  fruit  we  can  estimate  in  dollars 
or  boxes  of  lemons  the  actual  losses  and  savings,  while  in  the  orchard 
results  are  of  a  more  general  nature.  If,  therefore,  in  the  succeeding 
paragraphs  on  the  handling  of  the  fruit  in  the  house,  we  seem  to  show 
more  definite  results  than  in  the  discussion  of  methods  for  the  orchard, 
we  would  state  emphatically  that  this  is  not  the  case,  but  that  the 
methods  of  orchard  treatment  described  have  been  worked  out  and 
tested  with  the  same  degree  of  accuracy  and  completeness  as  those  for 
the  packing  house,  and  are  fully  as  valuable  and  important.  It  would 
be  most  desirable  could  we  overcome  the  trouble  entirely  in  the  orchard 
by  eliminating  the  source  or  possibility  of  infection,  and  this  is  feasible 
to  a  very  large  extent  by  the  simple  cultural  means  described.  Under 
actual  conditions,  however,  especially  in  the  associations  wThere  fruit 
from  many  different  orchards  comes  to  the  house,  this  can  be  only  par- 
tially accomplished,  and  in  every  case  wre  must  apply  every  possible 
means  to  bring  about  as  complete  a  control  of  the  rot  as  possible. 

In  discussing  the  nature  of  the  brown  rot  and  the  manner  in  which 
lemons  become  infected,  we  have  stated  that  there  are  three  sources  of 
infection:  In  the  orchard,  in  the  washer,  and  by  contact.  The  last 
two  come  under  the  consideration  of  control  in  the  packing  house. 

Prevention  of  Washer  Infection. 

We  have  shown  that  the  washing  machine,  in  which  the  fruit  is  sub- 
merged in  a  tank  of  water,  is  by  far  the  most  prolific  source  of  infection 
with  brown  rot.  The  water  becomes  infected,  not  by  the  fewT  affected 
lemons  which  go  through,  but  by  the  dust  and  dirt  from  the  orchard 
brought  in  with  the  boxes  and  fruit,  in  which  the  spores  of  the  fungus 
are  abundant.  In  this  manner  the  wash  water  becomes  filled  with 
spores,  and  infects  with  brown  rot  a  large  amount  of  previously  sound 
fruit.  This  source  and  manner  of  infection  was  the  first  discovered 
in  the  investigation,  and  much  attention  has  been  paid  to  its  exact 


Bulletin  190. 


BROWN   ROT    OP   THE   LEMON. 


45 


nature  and  means  of  prevention.  In  attacking  a  problem  of  this  sort 
the  most  natural  method  was  along  the  line  of  disinfecting  the  wash 
water  with  some  substance  which  would  destroy  the  fungus  without 
injuring  the  fruit,  and  this  has  been  the  nature  of  our  work  in  this 
direction.  The  first  experiments  showed  that  infection  could  be  very 
easily  prevented  in  this  manner,  the  chief  points  to  determine  being 
what  substance  to  use,  and  in  what  strength.    One  of  the  most  important 


f 


I 


; 


FIG.   24.     Bucket-soaking  method  of  disinfection  experiments. 

considerations  was  that  of  economy,  since  the  ordinary  washer  holds 
1,000  gallons,  and  with  the  losses  and  additions  during  a  day's  run 
much  more  than  that  quantity  is  used.  The  determination  of  the  best 
substances  and  strengths  to  be  used  for  the  purpose  of  wash-water 
disinfection  has  occupied  a  large  share  of  our  attention,  and  has  been 
carried  to  a  very  satisfactory  conclusion.  A  very  large  number  of 
experiments  have  been  carried  out  under  all  sorts  of  conditions,  and 


46  UNIVERSITY   OF  CALIFORNIA EXPERIMENT   STATION. 

with  many  different  objects  in  mind,  in  order  that  these  points  might  be 
thoroughly  worked  out. 

Of  the  disinfectants  in  common  use,  copper  sulphate  (bluestone), 
formalin  and  potassium  permanganate  have  received  our  principal 
attention,  seeming-  to  suit  the  purpose  best.  The  following  method  of 
experiment  was  adopted:  Four-gallon  buckets  were  filled  with  water, 
and  the  water  infected  with  the  brown-rot  fungus.  Infection  was 
accomplished  in  the  earlier  experiments  by  soaking  several  affected 
lemons  in  the  water  over  night,  and  rubbing  off  all  the  fungous  growth 
from  the  surface  into  the  water  next  morning.  Water  is  made  very 
highly  infectious  in  this  manner.  In  the  later  work,  after  the  infectious 
nature  of  orchard  soil  was  discovered,  the  buckets  of  water  for  the 
experiments  were  infected  by  placing  in  each  about  a  pint  of  soil  from 
ground  known  to  contain  the  fungus.  This  could  be  taken  almost  any- 
where in  an  orchard  during  the  winter,  but  as  the  dry  season  advanced 
it  was  necessary  to  get  soil  from  beneath  the  trees,  and  from  August 
to  the  beginning  of  the  rainy  season  soil  from  any  source  gave  very 
uncertain  infection.  After  infecting  a  sufficient  number  of  buckets  for 
the  experiment  in  hand  in  this  manner,  the  water  was  poured  back  and 
forth  from  one  to  the  other  until  thorough  mixing  had  been  accom- 
plished, in  order  that  the  infection  might  be  uniform.  Any  disinfectant 
to  be  tested  was  then  added  to  the  buckets  in  the  desired  strength,  and 
a  certain  number  of  good  lemons  placed  in  each  bucket.  (Fig.  24.) 
Check  buckets  were  left  in  each  case  without  any  disinfectant,  in  order 
to  show  that  the  water  was  properly  infected.  Ordinarily  in  every 
experiment  the  checks  would  not  only  show  100%  of  brown  rot,  all 
the  lemons  becoming  affected,  but  every  lemon  would  be  infected  in  a 
great  many  different  places.  (Fig.  10.)  The  good  lemons  were  soaked 
long  enough  to  insure  infection,  2  to  24  hours,  or  usually  over  night; 
then  taken  out  of  the  water,  placed  in  boxes,  and  put  away  in  a  tent 
for  the  rot  to  develop,  being  examined  frequently,  and  held  for  at  least 
a  month  for  all  the  decay  to  show  itself.  Many  experiments  were  also 
made  in  the  machine  itself,  and  in  many  other  ways,  of  which  those  of 
most  importance  will  be  alluded  to.  The  time  of  soaking  in  the  buckets 
is  very  excessive  compared  to  the  fifteen  or  possibly  thirty  minutes 
which  lemons  remain  in  the  washer  during  the  ordinary  washing,  but 
the  idea  was  to  make  the  test  a  severe  and  thorough  one.  Besides  the 
disinfectants  mentioned,  experiments  were  made  with  boric  acid, 
salicylic  acid,  sodium  benzoate  and  sulphide  of  potash,  but  none  of 
these  substances  appeared  to  be  worthy  of  much  consideration  for  our 
purpose. 

Experiments  with  Formalin. — This  substance  is  a  colorless  liquid. 
and   has  well-known   disinfectant  powers.     It  was  tested  by  adding 


Bulletin  190.  BROWN  ROT  OF  THE  LEMON.  47 

definite  amounts  to  the  buckets  of  infected  water,  and  then  soaking 
good  lemons,  while  certain  buckets  containing  good  lemons  in  infected 
water,  without  any  formalin,  were  held  as  checks.  It  was  found  that 
when  used  above  a  certain  limit  of  strength  lemons  were  very  badly 
injured  by  this  substance.  If  the  solution  w^s  too  strong  the  rind 
became  pitted,  spotted,  and  the  fruit  completely  spoiled.  This 
depended  on  the  time  of  soaking  as  well  as  the  strength  of  the  solution, 
a  weaker  strength  causing  injury  by  long  soaking.  Below  a  certain 
strength,  however,  the  fruit  can  be  soaked  in  the  solution  indefinitely 
without  burning. 

One  of  the  striking  results  of  these  soaking  experiments  with  formalin 
was  the  large  amount  of  blue-mould  (Penicillium)  rot  which  always 
occurred  on  fruit  injured  by  the  solution.  The  condition  was  the  same 
as  that  produced  by  bruising ;  lemons  injured  by  too  strong  a  treatment 
almost  invariably  became  affected  by  this  form  of  decay.  The  most 
interesting  point  was  the  fact  that  visible  spotting  or  burning  of  the 
lemon  was  not  necessary  to  produce  this  susceptibility  to  Penicillium. 
With  strengths  of  formalin,  or  periods  of  soaking  just  under  that 
necessary  to  produce  visible  injury,  a  large  part  of  the  treated  fruit 
would  go  down  with  blue  mould,  while  that  given  less  severe  treatment 
retained  its  normal  resistance.  The  natural  explanation  of  this  occur- 
rence is  that  treatment  just  below  the  limit  of  visible  injury  had  still 
so  weakened  or  killed  the  outer  rind  of  the  lemon  that  its  resistance  to 
the  attacks  of  the  mildly  parasitic  fungus  had  been  largely  destroyed. 
(See  experiments  1-48,  1-61,  II-4.)  It  is  noteworthy,  however,  that  in 
the  experiments  with  copper  sulphate,  and  other  disinfectants,  so  far 
as  they  were  tested,  this  result  did  not  appear. 

The  strength  of  formalin  solution  in  which  lemons  can  be  safely 
washed,  without  danger  of  injury,  can  be  stated  at  about  1-20%.  (One 
part  to  2,000,  or  one  pint  to  250  gallons  of  water.)  1-10%  shows  no 
bad  effect  in  one  hour's  soaking,  but  produced  both  a  slight  burning  and 
excessive  blue  mould  in  longer  treatments,  so  we  can  not  recommend 
the  solution  for  use  as  strong  as  this. 

For  controlling  brown-rot  infection  less  strengths  than  this  have  been 
effective.  In  every  case  in  the  bucket  experiments  strengths  down  to 
1-100%  (1  part  to  10,000,  or  1  pint  to  1,250  gals.)  have  completely 
checked  infection,  while  1-200%  has  shown  almost  as  good  results,  with 
practically  no  rot  except  a  doubtful  case  in  one  experiment.  These 
results  were  obtained  from  many  different  experiments  and  repetitions, 
and  checked  in  every  case  with  tests  of  the  same  water  with  no  disin- 
fectant, resulting  under  the  latter  conditions  in  100%  of  infection  of 
the  nature  shown  in  figure  10.  In  the  washer  itself,  infected  with  a 
bucketful  of  orchard  soil  in  the  water,  which  is  an  extreme  test,  a 
strength  of  1-50%  (1  pint  to  625  gallons)  has  seemed  necessary  for 
4— bul.  190 


4-8  UNIVERSITY   OF  CALIFORNIA EXPERIMENT   STATION. 

complete  disinfection  in  every  case.     We  would,  therefore,  not  recom- 
mend the  use  of  less  than  this  strength  in  practical  operations. 

Formalin  has  not  come  into  general  use  to  any  extent  for  washer 
disinfection.  It  is  somewhat  more  expensive  than  other  substances 
which  give  good  results,  and  not  as  powerful  in  effect,  requiring  greater 
strengths  to  accomplish  the  same  result.  There  is  also  some  prejudice 
against  its  use  on  the  part  of  most  lemon  men,  on  account  of  the  injury 
to  the  fruit  which  results  from  the  use  of  too  strong  a  solution.  This 
injury  can  be  entirely  avoided  by  using  a  proper  strength,  under  which 
conditions  burning  of  the  fruit  or  susceptibility  to  blue  mould  is  not. 
so  far  as  we  know,  produced  by  formalin  in  the  slightest  degree.  It 
has  the  advantage  of  being  a  clear  solution,  with  no  danger  of  staining 
the  fruit,  and  has  no  corrosive  action  on  the  metal  of  the  tank.  The 
matter  of  expense  is  an  objection  to  its  use,  though  this  is  by  no 
means  prohibitive.  It  costs  four  or  five  times  as  much  as  bluestone  and 
must  be  used  about  50%  stronger,  making  the  total  expense,  with  a 
full-sized  tank  running  continuously,  about  75  cents  per  day.  With 
the  1,000-gallon  tank,  one  and  one-half  pints  of  formalin  should  be 
poured  into  the  water  in  the  morning,  and  mixed  well  with  it.  If 
running  all  day,  put  in  another  pint  after  noon,  in  the  same  water. 

Experiments  with  Permanganate  of  Potash. — This  substance  has 
been  found  to  give  considerable  satisfaction  for  the  purposes  under 
discussion,  and  has  been  used  thus  far  in  the  lemon  houses  more  gen- 
erally than  any  other  disinfectant.  It  is  a  crystalline  substance  of  a 
dark  purplish  color,  readily  soluble  in  water,  to  which  it  gives  a  very 
intense  color.  A  very  small  amount  of  the  permanganate  will  color 
deeply  a  large  amount  of  water.  The  danger  in  the  use  of  too  strong 
a  solution  on  lemons  lies  in  the  possibility  of  staining  the  fruit,  rather 
than  that  of  burning  or  otherwise  injuring  it. 

Permanganate  is  mild  in  effect  compared  with  formalin  or  bluestone. 
It  does  not  corrode  iron.  The  staining  effect  is  seen  especially  on  rough, 
scarred  fruit,  on  which  the  scars  take  up  the  stain  very  readily,  and 
are  made  prominent.  1-50%  (1  pound  to  625  gallons)  is  about  as 
strong  as  this  substance  can  be  used  in  the  washer,  without  some  slight 
discoloration  of  the  scars  and  butts  of  the  lemons.  Even  1-200% 
causes  slight  staining  with  long  soaking,  but  the  strength  first  men- 
tioned is  safe  in  ordinary  washing.  In  bucket-soaking  experiments 
1-200%  (1  pound  to  2,500  gallons)  has  almost  always  produced  com- 
plete disinfection.  This  strength  is  close  to  the  minimum,  however.  In 
experiments  with  the  washer,  with  a  large  volume  of  badly  infected 
water  and  a  good  deal  of  fruit,  a  strength  nearly  up  to  1-50%  has 
seemed     necessary    to     insure     complete     disinfection,     although     less 


Bulletin  190.  BROWN  ROT  OF  THE  LEMON.  49 

strengths  were  usually  effective.  (See  Figs.  25  and  26.)  Early  in  our 
work  we  recommended  permanganate  of  potash  for  washer  treatment 
above  any  other  substance,  and  it  has  been  most  generally  used.  The 
strength  used  has  averaged  from  about  1  pound  to  1,000  gallons 
(1-80%)  to  8  ounces  to  1,000  gallons  (1-160%),  putting  in  three 
quarters  of  this  quantity  in  the  morning  and  the  balance  in  the  after- 
noon. In  most  cases  this  has.  given  good  satisfaction,  and  all  infection 
in  the  washer  has  been  completely  checked.  There  have  been  instances, 
however,  with  fruit  coming  from  very  badly  infected  orchards  on 
heavy  soil,  where  even  the  greater  strength  given  above  has  not  pro- 
duced complete  disinfection,  as  proven  by  actual  tests  of  the  wash 
water.  (See  experiment  11-16.)  This  fact  has  tended  to  weaken  our 
confidence  in  the  permanganate  treatment  somewhat,  inasmuch  as  the 
use  of  more  than  one  pound  to  1,000  gallons  is  objectionable  on  account 
of  the  deep  color  produced.  On  account  of  the  uncertainty  of  effect 
we  no  longer  urge  the  use  of  permanganate,  though  several  houses  are 
still  using  it  with  perfect  satisfaction. 

The  method  of  using  the  permanganate  is  to  weigh  out  the  requisite 
amount,  dissolve  it  in  a  bucket  of  water,  and  pour  into  the  tank.  We 
would  advise  those  using  it  to  use  a  pound  in  the  morning,  and  8  ounces 
more  in  the  afternoon  to  1,000  gallons.  The  substance  should  be  care- 
fully weighed  out,  and  no  guesswork  indulged  in,  as  the  estimation  of 
the  strength  of  the  permanganate  solution  by  its  color,  a  method  in 
which  some  have  come  to  think  themselves  infallible,  is  far  from  an 
accurate  one.  The  cost  of  the  material  is  about  20  cents  to  30  cents 
per  pound. 

Experiments  with  Copper  Sulphate.— The  disinfectant  properties 
of  copper  sulphate,  or  bluestone,  are  too  well  known  to  need  explana- 
tion, and  this  material  has  been  used  quite  extensively  in  our  work.  It 
has  proven  the  best  available  substance  for  the  present  purpose.  While 
having  some  faults,  it  is  cheap,  effective,  and  can  be  used  in  the  great- 
est strength  necessary  without  the  slightest  injurious  effect  upon  the 
fruit.  It  is  the  most  powerful  of  the  disinfectants  experimented  with, 
producing  disinfection  at  a  less  strength  than  any  of  the  other  sub- 
stances. At  the  same  time  it  is  considerably  cheaper,  costing  normally 
about  6  cents  a  pound,  though  recently  it  has  been  up  to  9  cents  and 
12  cents.  The  effect  of  too  strong  a  solution  of  bluestone  upon  lemons 
is  to  burn  and  pit  the  fruit  very  badly.  Its  effect  is  extremely  bad  in 
this  way  when  not  sufficiently  diluted.  1-20%  (1  pound  to  250  gal- 
Ions)  produces  no  apparent  injury  in  several  hours'  soaking,  though 
we  would  hardly  recommend  the  use  of  this  strength.  1-50%  is 
entirely  safe. 


50  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION. 

The  use  of  bluestone  for- washer  disinfection  is  complicated  by  a 
factor  not  met  with  in  the  use  of  the  other  substances  discussed.  This 
is  the  strong  affinity  of  the  material  to  combine  with  alkaline  substances 
in  the  wash  water,  and  with  the  iron  of  the  tank;  this  is  an  important 
consideration.  With  the  minute  quantities  of  copper  sulphate 
employed,  an  amount  which  would  produce  complete  disinfection  in 
distilled  or  fairly  soft  Avater  in  a  wooden  bucket  might  be  entirely 
precipitated  and  neutralized  by  the  alkali  in  a  harder  water,  or  by  the 
metal  of  an  iron  tank.  We  can  not  therefore  draw  the  figure  too  fine 
for  the  minimum  strength  necessary  to  disinfect,  but  must  allow  for 
any  condition  which  is  likely  to  occur.  So  far  as  disinfection  is  con- 
cerned this  is  not  a  serious  problem,  as  the  material  is  cheap,  and  we 
can  use  without  clanger  a  strength  sufficient  to  hold  its  own  in  any  water 
likely  to  be  used.  A  more  serious  matter,  and  the  only  real  objection 
to  the  use  of  bluestone,  is  the  injurious  effect  upon  the  tank.  This  has 
deterred  some  houses  from  the  use  of  this  material.  Still,  it  is  possible 
to  prevent  this  quite  largely  by  keeping  the  inside  of  the  tank  covered 
with  asphalt  paint,  and  the  use  of  bluestone  is  otherwise  so  satisfactory 
that  this  objection  has  not  seemed  a  very  serious  one  in  most  of  the 
lemon  houses.  Indeed,  it  would  be  much  cheaper  to  buy  a  new  tank 
at  very  frequent  intervals  than  to  take  a  chance  of  allowing  the  rot  to 
spread  in  the  washer.  The  injury,  however,  is  not  a  severe  one,  and 
by  painting  the  inside  of  the  tank,  as  just  mentioned,  its  life  is  very 
little,  if  any,  short  of  the  normal.  In  machines  with  a  wooden  tank 
this  difficulty  does  not  occur. 

In  distilled  or  fairly  soft  water  an  extremely  dilute  solution  of  copper 
sulphate  is  sufficient  to  kill  the  Pythiacystis  fungus  and  prevent  infec- 
tion. Strengths  of  1-500%  (1  part  to  50,000,  or  1  pound  to  6.250 
gallons)  have  almost  always  given  complete  disinfection  in  ordinary 
water,  with  the  checks  showing  100%  rot,  while  1-1,000,  1-2,500,  and 
even  1-5,000%  (1  part  to  500,000,  or  1  pound  to  62,500  gallons),  have 
often  checked  infection  completely  and  always  very  much  reduced  it. 
With  distilled  water  in  a  wooden  vessel,  infected  with  a  pure  culture 
of  the  fungus,  our  experience  gives  reason  to  believe  that  one  part  of 
bluestone  in  one  million  of  water  would  show  decided  disinfection.  In 
practice,  with  a  more  or  less  alkaline  water,  metal  tank  and  washer 
parts,  and  much  soil  and  other  matter  in  the  water,  it  is  not  safe  or 
desi rattle  to  attempt  the  use  of  any  such  weak  strengths  as  these, 
'-specially  when  15  cents'  worth  of  bluestone  per  day  will  afford  com- 
plete protection  from  any  possibility  of  infection  in  the  washer.  We 
have  already  slated  that  a  strength  of  1-50%  (1  pound  to  625  gallons) 
is  perfectly  safe  to  use,  so  far  as  any  damage  to  the  fruit  is  concerned, 
fmd  some  houses  are  using  the  solution  as  strong  as  this  as  a  regular 
prael  ice. 


8f'"'  ' 

... 

h. 

1 

1 

FIG.  25.     Result  of  infection  of  washer  with  orchard  soil.     Brown-rot  lemons 
at  the  left.     From  Bui.   184,  Cal.  Agr.  Expt.   Sta. 


• 

^ - ' 

• 

1        .  ■      -                                     9 

< 

" 

0 

FIG.   26.     Lemons  washed  in  same  water  as  those  in  Fig.   25,  after  disinfection 
of  water.     From  Bui.   184,  Cal.  Agr.  Expt.  Sta. 


•-1*-  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION. 

At  presenl  we  recommend  copper  sulphate  as  the  best  substance  for 
use  in  disinfecting  the  tank  against  infection  with  brown  rot.  Its 
only  fault  is  the  corrosive  action  on  iron,  but  if  the  inside  of  the  tank 
is  kept  well  painted  this  is  not  a  very  serious  one.  It  is  absolutely 
effective  at  a  strength  well  below  that  which  causes  injury  to  the  fruit, 
and  is  cheap,  colorless,  and  with  no  undesirable  effect  of  any  kind  except 
the  one  mentioned.  As  the  proper  strength  for  general  use  we  would 
recommend,  to  1,000  gallons  of  water,  about  16  ounces  of  bluestone  in 
the  morning,  with  8  ounces  more  added  in  the  afternoon.  The  material 
dissolves  rather  slowly  in  cold  water,  so  it  is  best  to  keep  a  stock  solution 
on  hand  in  a  barrel.  This  solution  may  be  made  in  the  strength  of 
two  pounds  to  the  gallon.  To  take  out  one  pound  of  bluestone  it  is  then 
necessary  to  dip  out  one-half  gallon  of  the  stock  solution.  For  8  ounces 
of  bluestone,  take  one  quart,  and  in  the  same  proportion  for  other 
amounts.  It  is  very  essential  to  keep  the  stock  solution  at  the  proper 
strength,  and  figure  correctly  how  much  to  use.  In  the  whole  operation 
of  washer  disinfection  and  washing  with  these  chemical  solutions,  the 
operator  should  know  accurately  at  all  times,  in  pounds  and  gallons, 
just  what  he  has  in  the  tank.  The  system  of  judging  the  strength  of 
the  solution  by  the  color  of  the  water,  or  any  other  guesswork  method, 
should  not  be  tolerated  if  satisfactory  results  are  to  be  obtained. 

Fumigating  the  Washeb. 

One  of  the  first  methods  resorted  to  by  lemon  men  in  attempting  to 
control  the  brown  rot  was  the  fumigation  of  the  washer  at  frequent 
intervals  with  burning  sulphur,  formalin  gas  or  hydrocyanic  acid  gas. 
The  empty  tank  was  covered  with  a  canvas,  and  the  gas  produced  inside. 
This  method,  when  the  water  was  not  being  disinfected,  has  at  times 
shown  decided  results  in  checking  rot  infection.  Particularly  with 
sulphur,  when  the  machine  was  treated  with  very  strong  fumes  at  times 
of  abundant  rot,  a  marked  diminution  in  the  amount  of  infection  often 
resulted  following  the  treatment.  Usually  the  amount  of  rot  decreased 
immediately  after  the  sulphuring,  but  began  at  once  to  increase  again. 
O  r-<a  si  on  ally  a  treatment  of  this  sort  in  early  summer,  just  at  the  end 
of  the  normal  brown-rot  season,  has  shown  decided  results  in  bringing 
the  prevalence  of  the  trouble  to  an  end.  These  effects  are  due  probably 
to  the  killing  of  the  fungus  growing  in  the  machine  itself.  So  long  as 
the  spores  are  being  continually  introduced  with  every  box  of  fruit, 
this  effect  is  very  short-lived  and  of  no  practical  value,  but  when  the 
fungus  is  becoming  less  abundant  and  nearly  lifeless  in  the  soil  at  the 
end  of  its  season,  fumigation  of  the  washer  shows  its  best  results.  In 
event  this  treatment  is  quite  needless,  if  the  water  is  kept 
thoroughly  disinfected. 


Bulletin  190.  BROWN  ROT  OF  THE  LEMON.  53 

General   Considerations   Regarding   Washer   Disinfection. 

By  thorough  disinfection  of  the  wash  water  brown  rot  can  in  most 
cases  be  almost  entirely  eliminated  from  the  fruit  in  the  house.  So 
effective  has  this  treatment  been,  that  in  a  single  season  the  brown  rot 
has  been  completely  overcome  in  many  houses  which  formerly  were  in 
a  deplorable  condition  and  losing  thousands  of  dollars  each  year  from 
this  cause.  By  the  expenditure  of  a  few  cents  per  day  for  bluestone  in 
the  wash  water  the  trouble  has  been  checked  at  its  very  source.  With 
improved  conditions  in  the  orchards,  the  success  with  which  the  problem 
is  being  met  will  be  even  greater.  In  cases  where  washer  disinfection 
does  not  reduce  brown  rot  in  the  house  to  a  minimum,  the  manager 
may  be  sure  that  one  of  two  things  is  the  trouble :  he  either  is  not 
disinfecting  the  water  completely,  or  a  large  amount  of  rot  is  coming 
in  from  the  orchard  in  such  an  undeveloped  condition  that  it  is  not 
apparent.  The  former  condition  may  be  easily  detected.  This  is  most 
readily  done  by  laying  aside  in  a  moist  place  some  of  the  lemons  which 
are  found  sunk  to  the  bottom  of  the  tank  at  night.  There  is  always 
a  considerable  number  which  do  this  during  the  day,  and  these,  if  any. 
will  contract  the  rot  if  there  is  any  infection  from  the  water.  If  these 
bottom  lemons,  after  keeping  them  a  week  or  two,  show  an  abundance 
of  brown  rot,  it  may  be  taken  as  sure  proof  that  the  water  is  not  being 
disinfected.  We  feel  sure  that  such  a  case  has  not  occurred,  and  will 
not  occur,  under  the  use  of  bluestone  in  the  strength  recommended.  It 
has  occurred  with  permanganate,  at  a  strength  beyond  which  it  is  not 
desirable  to  go  on  account  of  the  color,  and  may  occur  with  any  disin- 
fectant if  used  too  weak.  In  such  cases  we  strongly  advise  the  use  of 
bluestone  at  a  strength  of  24  ounces  to  1,000  gallons,  divided  into 
morning  and  afternoon  portions  of  16  and  8,  as  described  above.  If 
there  is  an  objection  to  this  for  any  reason,  we  suggest  formalin  as  next 
best,  practically  a  sure  disinfectant,  but  more  expensive  than  bluestone. 
Two  and  a  half  pints  per  day  in  1,000  gallons,  used  as  directed  in  the 
paragraph  on  the  subject,  should  give  good  results.  Permanganate 
seems  to  be  more  uncertain  in  effect  than  either  of  the  others,  and 
can  not  be  increased  sufficiently  in  strength  to  insure  absolute  disinfec- 
tion in  refractory  cases  without  producing  an  objectionable  color. 

One  of  the  results  of  incomplete  disinfection  is  usually  a  retarding  of 
the  development  of  the  rot,  so  that,  where  otherwise  it  would  show 
plainly  in  the  fruit  within  a  week,  it  straggles  along  for  two  or  three. 
This  has  been  a  very  marked  feature  of  our  experiments  when  a 
strength  of  the  disinfectant  was  reached  which  only  partially  disin- 
fected, and  the  same  thing  has  appeared  in  packing  houses  where  the 
disinfection  of  the  washer  was  found  to  be  incomplete.  (See  experi- 
ments 1-84,  1-88.)     This  is  worse  than  no  disinfection  at  all,  since  the 


54  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 

subsequent  handling-  0f  the  rot  is  more  difficult  on  account  of  this 
delayed  development.  It  is,  therefore,  an  excellent  plan  to  keep  a 
check  on  the  disinfection  by  saving  out  occasionally  the  bottom  lemons 
at  night.  They  should  not  develop  brown  rot  any  more  than  the  others, 
if  the  water  is  being  properly  treated.  Another  good  test  is  to  leave 
the  water  in  the  tank  over  night  after  the  day's  run,  and  let  a  number 
of  good  lemons  soak  in  it.  If  these  develop  infection  after  keeping  a 
week  or  two,  the  water  is  not  thoroughly  disinfected. 

In  general,  it  is  evident  that  the  amount  or  strength  of  any  disin- 
fectant necessary  to  keep  the  water  perfectly  free  from  danger  varies 
considerably  at  different  times,  according  to  the  season,  temperature, 
and  character  of  the  water,  amount  of  sediment,  abundance  of  the 
fungus  in  the  orchard  from  which  the  fruit  comes,  and  other  considera- 
tions. It  is,  therefore,  best  to  use  the  disinfectant  at  the  maximum 
strength  for  safety  to  the  fruit,  rather  than  at  the  minimum  of  possible 
disinfection.  We  strongly  urge  the  use  of  the  strongest  solutions  recom- 
mended, even  though  in  most  cases  a  considerably  weaker  solution 
would  be  effective.  The  material  is  too  cheap  to  take  any  chances  in 
a  matter  of  such  great  importance.  The  effect  on  the  tank  is  also  of  no 
consequence  compared  with  the  saving  of  the  fruit.  Again,  we  would 
urge  the  greatest  care  in  measuring  and  weighing  out  the  materials 
carefully  and  accurately  at  all  times,  not  depending  on  guesswork  for 
anything. 

In  case  the  wTater  is  being  thoroughly  disinfected,  and  still  a  la 
amount  of  brown  rot  develops  in  the  tents,  the  conclusion  may  be 
reached  that  this  is  orchard-infected  fruit  in  which  the  rot  had  not 
advanced  far  enough  to  show  itself.  This  may  occur  abundantly  at 
times  from  certain  orchards,  but  only  for  a  limited  season,  such  as 
after  rains.  No  treatment  in  the  house  can  check  rot  of  this  kind,  as 
when  a  lemon  is  once  infected  nothing  can  prevent  its  decay.  (See 
experiments  1-53  and  1-83.)  Good  orchard  treatment  must  be  the  solu- 
tion of  this  problem.  If  the  ground  under  the  trees  is  well  covered  in 
winter,  and  cultivated  in  summer,  there  will  be  little  of  this  sort  of 
infection.  All  that  can  be  done  in  the  house  is  to  watch  the  fruit  care- 
fully as  it  goes  through  the  washer,  in  order  to  cull  out  all  that  show 
the  slightest  sign  of  rot. 

P  re  king  Bottom  Fuuit  Separately. 

An  excellent  practice  in  orchards  where  there  is  known  to  be  a 
large  a  mount  of  affected  fruit  on  the  trees  is  to  pick  the  tops  and 
bottoms  separately.  Most  of  the  infection  is  in  the  lower  fruit,  and 
by  keeping  this  by  itself  in  picking,  washing  and  curing,  we  avoid 
mixing  it  with  the  little-affected  top  fruit  and  save  much  handling  and 


Bulletin  190.  BROWN  ROT  OF  THE  LEMON.  55 

contact  infection  in  the  tents.  The  disinfection  of  the  wash  water 
should  be  made  especially  thorough  at  times  when  infection  is  active  and 
much  affected  fruit  in  evidence,  in  order  that  no  further  infection  may 
take  place  in  the  washer. 

HANDLING   OF   AFFECTED  FRUIT   IN   THE   HOUSE. 

In  spite  of  all  precautions,  a  certain  amount  of  brown  rot  may  occur 
in  the  tents  on  account  of  the  amount  of  the  fungus  existing  at  present 
in  our  orchards,  and  there  are  also  cases  where  the  methods  of  rot 
prevention  described  have  not  yet  been  put  into  practice  as  fully  and 
thoroughly  as  might  be.  It  will,  therefore,  be  of  value  to  describe  the 
most  successful  methods  in  use  for  handling  the  rot  in  the  house,  in 
case  one  has  to  make  the  most  of  circumstances.  These  methods  were 
mostly  in  use  before  this  investigation  began,  and  represent  a  high 
degree  of  intelligence  and  adaptability  to  circumstances  on  the  part 
of  those  who  developed  them. 

The  important  factor  in  the  Avhole  consideration  of  the  handling  of 
brown  rot,  after  it  has  started  in  the  house,  is  contact  infection.  No 
matter  how  much  rot  may  show  in  the  tent,  the  fact  is  positive  that  it 
all  started  either  in  the  orchard,  the  washer,  or  by  contact.  There  is 
no  possible  means  of  spread  in  the  tent  except  by  the  last  method. 
The  extreme  virulence  of  the  fungus,  however,  and  the  rapidity  with 
which  it  may  spread  by  simple  growth  from  fruit  to  fruit  in  the  box, 
makes  its  control  wThen  well  started  almost  a  hopeless  matter,  unless  the 
proper  methods  are  very  carefully  applied.  Carloads,  and  even  whole 
months '  pickings  of  lemons,  have  been  lost  by  some  houses  starting  with 
unchecked  washer  infection,  and  carried  along  by  handling  of  the 
affected  fruit,  which  increased  rather  than  checked  the  contact 
infection. 

The  key  to  the  situation  lies  in  the  segregation  and  separate  handling 
of  what  have  come  to  be  called  ' '  contacts ' ' ;  these  are  lemons  which 
show  no  signs  of  decay,  but  which  have  been  lying  in  contact  with 
affected  lemons  in  the  box.  In  the  first  experience  with  brown  rot, 
the  lemons  in  the  curing  boxes  were  simply  sorted  over  when  the  rot 
began  to  show  badly,  the  affected  ones  thrown  out,  and  the  apparently 
good  ones  put  back  in  the  tent  or  packed  and  shipped.  This  led  to  an 
enormous  and  inexplicable  amount  of  further  decay.  Although  all  the 
affected  fruit  seemed  to  Have  been  taken  out,  the  rot  would  develop  even 
more  abundantly  than  before,  the  fruit  would  be  again  sorted,  and 
again  the  rot  would  develop,  until  the  process  became  one  of  simply 
handling  over  the  fruit  time  after  time  until  it  had  practically  all 
rotted.  Several  hundred  boxes  of  apparently  sound  lemons  would 
gradually  dwindle  to  four  or  five  before  the  decay  finally  stopped 


56  UNIVERSITY    OF   CALIFORNIA EXPERIMENT    STATION. 

This  was  the  worst  feature  of  the  whole  situation,  and  when  the  cause 
and  manner  of  infection  and  spread  of  the  rot  were  entirely  unknown 
it  is  not  surprising'  that  extreme  discouragement  wras  felt  in  the  lemon 
business.  From  all  appearances,  new  infection  was  continually  taking 
place  in  the  tent,  and  the  prospect  of  finding  any  means  of  preventing 
this  seemed  very  poor  indeed.  It  seemed  like  a  decay  similar  to  blue 
mould,  of  a  very  much  more  virulent  nature,  as  though  the  spores  or 
germs  of  some  infectious  organism  were  present  in  extreme  abundance, 
like  those  of  Penici.lium,  causing  continual  infection  of  the  stored  fruit. 
In  the  less  systematically  conducted  houses  the  only  relief  for  this 
situation  seemed  to  be  to  pick  out  the  rotten  fruit  as  soon  as  curing 
could  be  effected  and  hurry  the  remainder  to  market,  taking  a  chance 
that  it  might  not  rot  too  badly  in  transit,  but  might  reach  the  retailer 
or  consumer  in  time  to  return  some  kind  of  a  profit.  The  effect  of  this 
system  on  the  market  and  on  the  reputation  of  California  lemons  may 
be  imagined.  In  the  better  class  of  houses  the  situation  was  studied 
very  closely  and  considerable  relief  found.  It  was  found  that  the  source 
of  the  continual  spread  of  the  trouble  in  the  house  was  contact  infection, 
and  that  fruit  which  did  not  develop  brown  rot  soon  after  being  put 
in  the  tent  remained  free  from  the  trouble  ever  after,  unless  it  had 
been  lying  in  contact  with  an  affected  lemon.  By  carefully  sorting  out 
these  ' '  contacts ' '  at  the  first  picking  over,  it  was  found  that  practically 
all  the  subsequent  rot  developed  in  them,  and  little  or  none  in  the 
lemons  which  had  not  been  in  contact  with  affected  ones.  In  other 
words,  it  was  found  necessary,  in  order  to  clean  the  fruit  of  brown  rot, 
to  take  out  all  lemons  which  had  been  touching  affected  ones,  as  well  as 
the  latter  themselves,  the  continued  spread  of  the  rot  having  come 
from  the  former  class  of  fruit.  By  doing  this  once,  or  possibly  twice, 
to  get  a  few  belated  cases  or  overlooked  "contacts,"  the  brown  rot 
could  be  eliminated  from  the  body  of  the  fruit.  The  process  was  then 
repeated  writh  the  ' '  contacts ' '  themselves,  the  affected  ones  being  picked 
out  after  a  sufficient  time  of  storage,  and  the  "contacts"  from  them 
again  segregated.  In  this  way  a  considerable  quantity  of  fruit  would 
be  released  from  quarantine,  and  restored  to  the  condition  of  the  good 
fruit  from  the  original  picking  over.  Thus,  by  close  and  careful  sorting, 
much  fruit  could  be  saved,  and  the  spread  of  the  rot  confined  to  a 
comparatively  small  amount.  The  system,  however,  was  a  very  laborious 
and  expensive  one.  Since,  when  the  rot  was  abundant  it  might  develop 
in  nearly  every  box  of  fruit  with  several  separate  originals  in  each 
box,  if  sorted  too  quickly  the  originals  would  not  have  all  developed, 
and  if  left  too  long  much  spread  by  contact  would  occur,  and  the 
expense  of  sorting  became  excessive.  Moreover,  the  condition  of  the 
good'  fruit  was  injured  by  so  much  handling,   the  amount  of  fruit 


Bulletin  190.  BROWN  ROT  OP  THE  LEMON.  57 

actually  lost  was  very  large  in  spite  of  the  most  careful  attention,  and 
the  house  became  filled  with  the  various  classes  of  fruit  made  in  the 
different  sortings.  This  much  was  accomplished,  however,  and  is 
worthy  of  record:  that  certain  houses,  although  troubled  with  brown 
rot  as  badly  as  any,  kept  the  rot  out  of  their  shipments  and  sent  to 
market  fruit  as  sound  and  of  as  good  keeping  quality  as  it  would  have 
been  if  brown  rot  had  never  been  heard  of.  Under  the  peculiarly  diffi- 
cult and  trying  circumstances  this  is  very  much  to  their  credit. 

Thorough  disinfection  of  the  washer,  and  proper  orchard  practice, 
have  eliminated  most  of  this,  but  a  description  of  the  best  methods  of 
handling  will  be  of  value.  When  brown  rot  is  occurring  in  the  fruit, 
it  should  be  watched  very  carefully  in  the  tent  in  order  not  to  allow 
contact  infection  to  spread  too  far.  The  first  sorting  should  take  place 
after  a  long  enough  period  has  elapsed  to  allow  the  original  rot  to 
develop,  but  not  long  enough  to  allow  it  to  spread  any  more  than  can 
be  avoided.  The  time  varies  with  the  season,  temperature  and  other 
conditions,  but  is  usually  from  ten  to  thirty  days,  more  of  ten.  nearer  the 
former  figure.  This  can  only  be  determined  by  watching  the  fruit. 
An  experienced  man  can  tell  by  the  odor,  and  the  gathering  of  flies  on 
the  boxes,  when  the  rot  is  getting  well  developed.  When  the  time  for 
sorting  comes,  the  boxes  are  taken  down  and  the  fruit  carefully  handled 
over  into  new  ones.  All  lemons  which  are  neither  affected  nor  touching 
affected  ones  are  simply  laid  over  into  the  other  box.  Blue  moulds  are 
thrown  out  and  the  lemons  in  contact  with  them  put  with  the  good,  as 
there  is  no  danger  from  them.  When  a  brown  rot  is  found,  the  sorter 
should  proceed  with  extreme  care.  All  the  sound  lemons  which  have 
the  least  suspicion  of  having  been  in  contact  with  one  that  is  affected, 
should  be  put  into  a  separate  box  as  ' '  contacts. ' '  The  affected  ones  are 
to  be  thrown  into  a  refuse  box,  and  hauled  away  to  a  place  not  in  any 
citrus  orchard  and  with  no  drainage  into  one.  If  a  lemon  shows  the 
slightest  infection,  even  the  minutest  spot,  it  should  be  thrown  out, 
as  it  will  invariably  go  down.  The  "  contacts, "  it  should  be  under- 
stood, are  lemons  which  do  not  show  any  sign  of  decay,  but  which  have 
simply  been  touching  affected  ones.  If  the  sorting  could  be  done  by 
an  expert,  he  could  no  doubt  put  many  of  these  in  with  the  good  with 
safety,  since  no  infection  takes  place  except  on  the  lemon  lying  in 
contact  with  the  affected  portion  of  another  and  the  fungus  actually 
growing  across,  but  with  average  labor  it  is  much  safer  to  have  every 
lemon  which  touches  at  all  put  with  the  "contacts."  The  chief  pre- 
caution necessary  is  to  prevent  the  "contacts"  from  rolling  away  from 
the  affected  lemons  by  careless  handling.  A  heedless  worker  has  the 
tendency  to  handle  over  the  fruit  from  box  to  box  mechanically,  and, 
before  he  notices  a  case  of  brown  rot,  will  take  away  the  lemons  around 


58  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 

it  and  let  the  "contacts"  roll  down  and  mix  with  the  good  fruit.  It 
is.  therefore,  advisable  to  leave  this  work  to  a  few  selected  men.  The 
best  system  is  to  let  the  general  help  take  down  the  boxes  and  transfer 
the  fruit  until  they  find  a  box  with  brown  rot:  as  soon  as  this  is  dis- 
covered, the  box  should  be  set  aside  and  left  for  special  men  to  handle. 

With  fruit  Avhich  contains  a  large  amount  of  rot  it  is  sometimes 
advisable  to  handle  it  in  trays  instead  of  boxes.  In  this  way  the  fruit 
is  in  one  layer  and  contact  can  take  place  only  in  one  direction.  The 
lemons  are  also  less  clcsely  pressed  together  than  in  a  box.  and  the 
amount  of  contact  is  reduced  for  this  reason.  The  chief  objections  to 
the  system  are  the  large  number  of  trays  required  to  handle  the  fruit, 
and  the  difficulty  of  handling  the  trays  without  allowing  the  lemons 
to  roll  about  and  thereby  losing  track  of  the  "contacts."  If  the  I 
can  be  provided  and  handled  carefully,  their  use  will  undoubtedly 
reduce  the  amount  of  contact  infection.  Some  handle  all  the  fruit 
directly  from  the  washer  in  trays  when  rot  is  abundant,  or  again  only 
the  lemons  from  badly  affected  orchards,  or  from  the  bottoms  of  the 
trees,  are  cured  in  this  way.  If  the  fruit  is  reasonably  free  from  rot, 
there  is  no  advantage  to  be  gained  from  the  use  of  trays.  The  practice 
is  quite  common  of ,  putting  the  "contacts"  onto  trays,  and  holding 
them  in  that  manner  for  the  rot  to  develop.  By  some  they  are  wrapped 
in  paper,  as  for  shipping,  and  put  back  into  boxes,  and  this  prevents 
further  spread  by  contact  quite  completely. 

The  whole  operation  of  handling  a  large  amount  of  brown  rot  in  the 
house,  checking  its  spread,  and  eliminating  it  from  the  fruit  is  laborious 
and  expensive  in  the  extreme.  It  is  only  with  the  greatest  care  that 
it  can  be  done  at  all  successfully.  The  system  is  very  simple,  however, 
and  depends  entirely  upon  the  thoroughness  with  which  the  contact 
lemons  are  taken  out  of  the  body  of  the  fruit  along  with  the  actual  rots. 
The  subsequent  proceedings  lie  chiefly  in  working  the  "contacts"  again 
by  the  same  method  in  order  to  save  as  many  of  them  as  possible.  AVith 
proper  treatment  in  the  orchard,  and  thorough  disinfection  of  the 
washer,  there  will  be  no  necessity  of  any  considerable  amount  of  this 
work,  and  in  these  directions  lies  the  only  rational  and  at  all  successful 
means  of  brown-rot  control. 


OTHER  FORMS  OF  CITRUS  DECAY. 

The  common  form  of  rot  in  all  citrus  fruit  is  that  caused  by 
Penicillhim,  commonly  referred  to  as  blue  mould.  This  fungus  is 
omnipresent  in  the  packing  houses,  and  rapidly  takes  possession  of  all 
bruised  or  weak  fruit.  It  is  not  an  active  parasite  and  gives  very  little 
trouble  with  sound  fruit  in  good  condition.  An  intimate  acquaintance 
with  citrus  decay  soon  leads  to  the  suspicion  that  there  are  two  different 


Bulletin  190.  BROWN  ROT  OF  THE  LEMON.  59 

species  of  Penicillium  present,  one  a  blue  green  and  the  other  an  olive- 
colored  mould,  with  differences  in  growth  as  well  as  color.  We  have 
substantiated  the  fact,  by  means  of  pure  cultures  and  inoculations,  that 
there  are  two  distinct  species.  The  nomenclature  of  these  forms  is  so 
uncertain  that  it  is  hardly  worth  while  to  discuss  names,  but  we  dis- 
tinguish the  two  species  as  P.  glaucum  Link,  for  the  blue  green,  and 
P.  digit atum  Fr.  for  the  olive  green.  The  characteristic  growth  of  the 
two  on  lemons  is  shown  as  well  as  can  be  done  in  a  photograph  in  figure 
27.  P.  glaucum,  on  the  left,  has  a  bright  bluish  color,  and  grows  char- 
acteristically, with  a  small  amount  of  surface  mould  in-  the  center  of 
a  softened,  rotten  area.  The  amount  of  surface  mould  which  it  forms 
is  very  much  less  than  in  the  other  species  (the  two  lemons  in  the 
picture  having  been  inoculated  at  the  same  time),  and  the  blue-green 


FIG.    27.      Forms   of  blue-mould    rot.      At  left  Penicillium   glaucum, 
at   right  P.   digitatum. 

spore  mass  develops  almost  as  fast  as  the  surface  mycelium,  which  is  at 
first  white.  The  characteristic  growth  of  glaucum  on  a  lemon,  therefore, 
consists  of  a  small  amount  of  bluish  mould  in  the  center  of  infection, 
a  very  narrow  edge  of  white  about  this,  and  an  outer,  wider  band  of 
softened  but  not  mouldy  lemon  tissue. 

P.  digitatum,  the  olive  species,  grows  rapidly  over  the  surface,  first 
as  a  white  mould,  which  later  turns  olive  from  the  center  rather  slowly. 
The  lemon  is  not  softened  outside  the  mouldy  area,  and  the  mould 
develops  over  the  surface  much  more  rapidly  than  in  the  other. 

Glaucum  is  more  actively  parasitic  than  the  second  species,  causing 
some  infection  by  contact.  Digitatum  is  the  more  common,  and  forms 
the  predominant  type  of  blue-mould  decay.  It  is  apparently  the  same 
form  as  that  described  by  the  writer  some  years  ago  as  being  found 
commonly  on  oranges  in  market  in  the  East.* 

*See  Botanical  Gazette,  Vol.  XXIV,  No.  2,  Aug.  1S9T,  pages  103  and  104. 


60 


UNIVERSITY    OP  CALIFORNIA EXPERIMENT   STATION. 


Another  not  uncommon  rot  is  that  shown  in  figure  28.  This  has  been 
given  the  name  of  "cottony  fungus,"  and  sometimes  causes  consider- 
able losses.  The  characteristic  of  this  form  of  decay  is  a  dense,  white- 
mould  growth,  which  spreads  very  rapidly  over  the  fruit  in  the  boxes. 
The  resulting  rot  is  decidedly  virulent,  large  masses  of  sound,  green 
fruit  being  involved.     If  the  trouble  was  more  common,  it  would  be 


FIG  2  8.     Cottony-mould  rot   (Sclerotinia) . 


a  very  serious  matter  indeed.  Practically,  however,  it  is  not  often 
abundant  enough  to  cause  much  concern.  The  fungus  is  a  species  of 
Sclerotinia.  In  the  white,  cottony-mould  growth  solid  black  bodies 
develop,  as  seen  in  the  illustration.  These  are  sclerotia,  a  stage  in  the 
development  of  the  fungus.  If  allowed  to  lie  for  a  time  on  moist  soil, 
they  throw  up  little  stalks  and  produce  funnel-shaped,  toadstool-like 
bodies,  which  contain  the  spores  of  the  fungus.     (Fig.  29.) 


Bulletin  190. 


BROWN   ROT   OF   THE   LEMON. 


61 


FIG.  29.     Spore-bearing  stage  of  the  cottony-mould  fungus. 
(Peziza  form  of  Sclerotinia.)     Natural  size. 


ILLUSTRATIVE  EXPERIMENTS. 

These  illustrations  are  chosen  from  the  large  number  of  experiments 
carried  out  during  the  progress  of  the  work,  as  showing  typically  the 
results,  and  the  methods  of  arriving  at  the  facts  upon  which  the  con- 
clusions given  in  this  bulletin  are  based.  All  the  results  given  were 
supported  by  many  other  experiments  of  a  similar  nature  and  a  variety 
of  tests  along  the  same  lines.  It  has  seemed  to  the  writer  that  a  more 
readable  publication  will  result  from  thus  grouping  the  specific  data 
of  most  of  the  experiments  in  an  appendix  form,  with  references  in  the 
text  from  time  to  time  to  the  experiments  upon  which  conclusions  are 
based,  rather  than  to  encumber  the  main  portion  of  the  bulletin  with 
the  detailed  methods  and  results  of  the  various  experiments. 


Soaking  Good  Lemons  in  Water  in  Which  Affected  Ones  Have  Been 
Soaked  Produces  Infection. 

Experiment  1-19 ;  July,  1905.  Soaked  several  lemons  having  brown 
rot  in  bucket  of  water  for  two  hours.  Removed,  and  put  in  15  good 
ones;  9  of  the  latter  became  affected  with  brown  rot. 

Did  the  same  with  Penicillium  rot.    No  infection  resulted. 

Experiment  1-31 ;  August,  1905.  A.  Soaked  one  lemon  affected  with 
brown  rot  in  bucket  of  water  for  twenty  hours.  Then  soaked  50  good 
lemons  in  same  water  for  ten  hours.    17  developed  brown  rot. 

B.  Soaked  20  affected  lemons  instead  of  one.  Otherwise  as  A.  Good 
lemons  all  took  brown  rot. 

Experiment  1-51 ;  August,  1905.  Infected  six  buckets  of  water  by 
soaking  affected  lemons.  In  A  soaked  50  good  lemons  fifteen  minutes ; 
1  brown  rot  resulted.    B.  Soaked  good  lemons  one-half  hour;  1  brown 


62  UNIVERSITY   OF   CALIFORNIA EXPERIMENT   STATION. 

rot.     C.   Soaked  good  lemons  one  hour;  13  brown  rots.    D.  Soaked  good 
lemons  two  hours;  30  brown  rots.     E.  Soaked  good  lemons  four  hours; 
33  brown  rots.    F.  Soaked  good  lemons  eight  hours;  50  (all)  brown  rots. 
See  also  cheeks  in  many  other  experiments. 

Boiling  Infected  Water  Prevents  Infection. 

Experiment  1-24;  July,  1905.  Soaked  a  box  of  lemons  affected  with 
brown  rot  in  a  tub  of  water  over  night.  In  the  morning,  boiled  half 
the  water  for  ten  minutes.  Then  placed  100  good  lemons  in  each 
portion,  boiled  and  unboiled,  and  soaked  over  another  night.  In  the 
unboiled,  79  became  affected  with  brown  rot;  in  the  boiled,  no  rot 
resulted. 

Affected  Lemons  Placed  on  Soil  Make  It  Infectious. 

Experiment  1-33 ;  August,  1905.  Dug  up  and  watered  a  plot  of 
ground  in  a  garden  away  from  any  citrus  trees.  On  one  half  the 
plot  laid  brown  rot-affected  lemons  all  over  the  surface;  none  on  the 
other  half.  Kept  both  plots  wet  for  twelve  days;  then  removed  the 
rotten  lemons  and  placed  80  good  ones  on  the  surface  of  each.  On  the 
infected  soil  all  but  two  of  the  good  lemons  took  brown  rot;  on  the 
uninfected  soil  no  brown  rot  resulted. 

See  also  experiments  on  soil  treatment.  (1-30.  1-65.  1-66,  1-80, 
1-83,  etc.) 

Infection  From  Pure  Culture. 

Experiment  II-10A;  January,  1906.  Soaked  50  good  lemons  for 
twenty-two  hours  in  a  bucket  of  water,  into  which  had  been  emptied 
a  flask  culture  of  Pythiacystis  citrophthora ;  84%  developed  brown  rot. 

Soaked  50  more  lemons  in  a  bucket  of  plain  water  as  a  check ;  no 
decay  resulted. 

Orchard  Soil  in  Water  Produces  Infection. 

See  experiments  on  soil  from  different  depths,  and  all  later  water- 
disinfection  experiments.     1-83,  1-96,  IY-17,  etc.,  etc. 

Wash  Water  May  Be  Infectious. 

Experiment  1-12;  July,  1905.  Soaked  5  boxes  of  lemons  (about 
1,000)  in  tank  of  wash  water  over  night;  all  but  10  lemons  developed 
brown  rot. 

Experiment  1-36;  August,  1905.  Soaked  50  good  lemons  in  wash 
water  and  sediment,  after  running  washer  all  day ;  29  developed  brown 
rot. 

Soaked  same  number  in  plain  water;  no  decay  developed. 


Bulletin  190.  BROWN  ROT  OP  THE  LEMON.  63 

Experiment  II-3;  July,  1905.  Soaked  lemons  which  had  just  been 
washed  as  follows:  126  lemons  in  plain  water  for  fifteen  hours,  3% 
brown  rot  developed ;  129  lemons  in  water  from  washer  for  fifteen  hours, 
80%  brown  rot  developed;  131  lemons  in  sediment  and  wash  water  for 
sixteen  hours,  100%  brown  rot  developed. 

Experiments  in  Infecting  Washer  With  Soil. 

Experiment  IV-1  (in  part)  ;  March,  1906.  Dumped  a  bucket  of 
infected  soil  into  the  washer  tank,  making  the  water  very  muddy.  Then 
ran  through  26  boxes  of  lemons  in  the  usual  manner;  991  lemons  with 
original  brown  rot  were  counted  out  during  the  following  six  weeks. 
(This  lot  is  shown  in  figure  25.)  Also  dipped  out  a  bucketful  of  the 
water,  and  soaked  50  lemons  in  it  for  two  hours ;  all  developed  brown 
rot. 

See  also  several  disinfection  experiments.    IV-11,  IV-14,  etc. 

Brown  Rot  Infection  From  Washer  Padding. 

Experiment  1-41 ;  August,  1905.  Soaked  pieces  of  sheepskin  padding 
and  rags  from  the  washer  in  a  bucket  of  water  over  night ;  then  soaked 
50  good  lemons  all  day  in  the  same  water ;  9  became  affected  with 
brown  rot. 

Brown-Hot  Tests  of  Soil  From  Different  Depths  and  Locations. 

Experiment  1-83;  September,  1905.  Tested  the  top  and  bottom  soil 
from  boxes  of  freshly  infected  earth.  Soil  from  surface  soaked  in 
water  with  good  lemons  gave  100%  brown  rot ;  soil  from  bottom  of  box, 
about  eight  inches  deep,  gave  88% ;  fruit  in  first  lot  completely  covered 
with  infections ;  not  so  abundant  in  second. 

Experiment  1-96;  September,  1905.  Soaked  a  small  quantity  of 
earth  from  following  depths  in  infected  ground  in  buckets  of  water 
with  good  lemons:  from  first  two  inches,  100%  brown  rot  produced; 
from  4  to  7  inches,  92%  brown  rot,  fewer  infections;  below  7  inches, 
44%  brown  rot,  fewer  infections  and  slower  development. 

Experiment  IV-17 ;  May,  1906.  Took  samples  of  soil  from  follow- 
ing locations,  and  soaked  each  in  bucket  of  water  with  50  good  lemons : 
Surface  soil  from  under  a  lemon  tree  in  an  orchard  where  the  ground 
under  the  trees  had  been  kept  well  stirred;  no  decay  resulted.  From 
under  a  tree  about  one  hundred  yards  from  the  last,  in  an  orchard 
where  the  ground  had  not  been  so  stirred;  100%  brown  rot.  From 
an  orchard  where  some  rot  occurred,  but  not  worst;  76%  brown  rot. 
From  another  part  of  same  orchard  where  rot  was  very  bad;  100% 
brown  rot.  From  an  orchard  near  last,  but  on  higher,  well-drained  soil ; 
no  decay.  Check — Plain  water  with  no  soil ;  no  decay. 
5— bul.  190 


64  UNIVERSITY   OF   CALIFORNIA — EXPERIMENT   STATION. 

Experiment  IV-28 ;  May,  1906.  Soaked  samples  of  soil  as  follows, 
in  buckets  of  water  with  good  lemons:  Soil  from  under  a  lemon  tree 
where  there  was  brown  rot  last  winter ;  produced  78%  brown  rot.  From 
bare  land,  a  few  rods  from  the  orchard ;  no  decay. 

From  another  orchard  where  no  brown  rot  had  been  seen  in  the 
fruit ;  no  decay. 

Experiment  IV-30 ;  May,  1906.  Took  samples  of  soil  from  each  of 
four  sides  of  a  lemon  tree  at  the  following  depths,  in  an  orchard  badly 
affected  with  brown  rot,  mixed  the  four  from  each  depth  together,  and 
soaked  in  a  bucket  of  water  with  good  lemons:  Surface,  produced 
100%  brown  rot;  6  inches,  88%;  12  inches,  66% ;  18  inches,  68%;. 
24  inches,  100%. 

Experiment  IV-31 ;  May,  1906.  Same  as  last,  from  another  orchard. 
Surface,  70%  ;  6  inches,  16%  ;  12  inches,  no  decay;  24  inches,  100' 

Experiment  IV-32;  June,  1906.  Same  as  last  two.  Surface,  100% 
brown  rot;  6  inches,  2%  ;  12  inches,  90%  ;  24  inches,  28%. 

Experiment  V-6 ;  June,  1906.  Took  samples  of  soil  at  different  dis- 
tances out  from  the  edge  of  a  lemon  orchard,  and  soaked  in  buckets  of 
water  with  good  lemons.  Surface  soil  under  tree  in  outside  row, 
100%  brown  rot;  6  feet  out  from  tree,  no  decay;  30  feet  out,  2%. 

Experiment  V-7 ;  June,  1906.  Test  in  usual  manner  of  soil  from 
different  depths  in  orchard  badly  affected  with  brown  rot.  Surface, 
96%  brown  rot;  24  inches,  no  decay;  36  inches,  no  decay;  42  inches,  no 
decay;  48  inches,  14%  ;  54  inches,  10%. 

Effect  of  Drying  Infected  Soil. 

Experiment  1-80;  September,  1905.  Infected  three  boxes  of  soil 
very  thoroughly  with  brown  rot,  so  that  good  lemons  laid  on  the  surface 
would  all  rot.  Then  allowed  the  soil  to  become  thoroughly  dry.  standing 
for  several  weeks.  After  this  the  soil  was  wet  up  again,  and  40  good 
lemons  laid  on  the  surface  in  each  box.  In  one  box  two  brown  rots 
developed ;  this  was  all  the  infection  that  took  place. 

Experiment  1-87;  September,  1905.  A  box  of  soil  was  made  very 
infectious,  and  then  dried  for  a  month.  Soaked  up,  and  placed  good 
lemons  on  the  surface ;  no  decay  developed. 

Chemical  Treatment  of  Infected  Soil. 

Experiment  1-30;  August,  1905.  Infected  the  soil  in  several  boxes 
with  brown  rot ;  then  made  the  following  applications  to  the  soil  in  each 
box.  and  put  40  good  lemons  on  the  surface:.  1.  Infected  soil,  no  treat- 
ment, 23  of  the  good  lemons  developed  brown  rot;  2.  Surface  covered 


Bulletin  190.  BROWN  ROT  OP  THE  LEMON.  65 

with  lime,  no  decay ;  3.  No  treatment,  31  brown  rots ;  4.  Surface  covered 
with  sulphur,  no  decay ;  5.  No  treatment,  32  brown  rots ;  6.  Soil  soaked 
with  3%  copper  sulphate,  no  decay. 

Experiment  1-65 ;  August,  1905.  Infected  soil  Used  in  experiment 
1-33  was  divided  into  two  plots :  A  was  well  soaked  with  1-12%  copper 
sulphate;  B  nothing.  Good  lemons  then  laid  on  the  surface  of  each. 
On  A,  94%  developed  brown  rot ;  on  B,  100%.  The  fungus  became  very 
abundant  on  the  surface  of  both  plots. 

Experiment  1-66 ;  August,  1905.  Prepared  three  boxes  of  infected 
soil,  and  soaked  A  with  1-10%  copper  sulphate,  B  with  1-100%,  and  C 
with  1-200% ;  then  laid  good  lemons  on  the  surface  of  each.  A 
developed  35%  brown  rot,  B  60%,  C  65%. 

Experiments  1-90  and  1-104 ;  September,  1905.  Soaked  ground  beneath 
a  lemon  tree  with  280  gallons  of  1-100%  copper  sulphate.  Two  weeks 
later  tested  the  soil  by  soaking  a  little  of  it  in  water  with  good  lemons  -y 
100%  brown  rot  resulted. 

Water  Disinfection  With  Formalin. 

Experiment  1-48 ;  August,  1905.  Placed  10  affected  lemons  in  each 
of  three  buckets  of  water,  and  soaked  seven  hours;  then  removed  and 
put  50  good  lemons  in  each;  also  added  to  A  formalin  to  make  1-5 %r 
and  soaked  over  night;  with  B  soaked  the  good  lemons  in  the  infected 
water  over  night,  then  in  1-3%  formalin  for  2  hours;  in  C  soaked  the 
50  good  lemons  in  infected  water  without  any  treatment,  as  a  check.  A 
developed  no  brown  rot,  lemons  slightly  burned  by  the  formalin,  70% 
blue  mould;  B,  100%  brown  rot;  C,  100%  brown  rot. 

Experiment  1-61 ;  August,  1905.  Infected  four  buckets  of  water  as 
in  last.  After  adding  disinfectant,  soaked  50  good  lemons  over  night  in 
each.  A,  formalin  1-5%,  no  brown  rot,  94%  blue  mould;  B,  formalin 
1-10%,  no  brown  rot,  52%  blue  mould;  C,  1-20%  formalin,  no  brown 
rot,  8%  blue  mould;  D,  check,  no  disinfection,  100%  brown  rot. 

Experiment  II-4;  July,  1905.  Soaked  100  lemons  in  each  of  follow- 
ing solutions  for  fourteen  to  sixteen  hours:  1%  formalin,  badly  burned, 
61%  blue  mould  developed;  1-2%  formalin,  burned,  41%  blue  mould; 
1-10%  formalin,  slightly  burned,  40%  blue  mould.  Water  not  infected 
with  brown  rot  in  these. 

Experiment  II-7 ;  December,  1905.  Water  infected  with  affected 
lemons.  Good  lemons,  soaked  twenty-two  hours;  1-200%  formalin,  2% 
brown  rot;  1-500%  formalin,  70%;  1-1,000%,  60%;  check,  100%. 

Experiment  II-10B ;  January,  1906.  Same  as  last.  1-100%  formalin, 
no  decay;  1-150%  formalin,  no  decay;  1-200%  formalin,  no  decay; 
check,  94%  brown  rot. 


66  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT   STATION. 

Experiment  IV-14;  April  1906.  Dumped  a  bucketful  of  infected 
orchard  soil  into  the  tank  of  a  washer,  making  the  water  very  muddy ; 
then  ran  through  10  boxes  of  lemons ;  90  original  brown  rots  developed 
in  these.  Also  soaked  50  lemons  in  a  bucketful  of  the  same  water  for 
three  hours;  all  developed  brown  rot. 

Then  put  into  the  same  water  in  washer,  formalin  to  make  1-500%  ; 
ran  through  another  10  boxes;  110  original  brown  rots  developed  in 
these.  Soaked  50  lemons  three  hours  in  a  bucketful  of  the  same  water ; 
28  developed  brown  rot. 

Then  put  into  the  same  water  in  washer  more  formalin  to  make 
1-125%  ;  ran  through  10  boxes  more;  78  original  brown  rots  developed 
in  these.  Soaked  50  lemons  three  hours  in  a  bucketful  of  the  same 
water;  5  developed  brown  rot. 

Experiment  IV-24;  May,  1906.  Same  method  as  last.  Infected 
washer  with  orchard  soil;  then  ran  through  6  boxes  of  lemons;  49 
developed  brown  rot.  Then  added  formalin  to  make  1-125%),  and 
washed  10  boxes  more ;  10  brown  rots.  Added  more  formalin  to  make 
1-40%,  and  washed  10  boxes  more;  no  brown  rot  developed  in  these. 

Water  Disinfection  With  Permanganate  of  Potash. 

Experiment  II-4;  July,  1905.  Soaked  100  lemons  for  fourteen  to 
sixteen  hours  in  each  of  the  following  solutions:  1-8%  permanganate, 
stained,  no  decay;  1-40%,  scars  stained,  no  decay;  1-160%,  sears 
slightly  stained,  no  decay. 

Experiment  II-6 ;  November,  1905.  Infected  buckets  of  water  with 
affected  lemons.  Soaked  good  lemons  in  them  for  three  and  a  half 
hours,  with  following  disinfections  and  results :  1-50%  permanganate, 
no  decay,  scars  stained;  1-100%,  no  decay,  scars  stained  slightly: 
1-200%,  no  decay  or  staining;  check,  no  disinfectant,  64%  brown  rot. 

Experiment  II-7;  December,  1905.  Same  as  last.  Good  lemons 
soaked  twenty-two  hours.  1-200%  permanganate,  no  brown  rot; 
1-500%,  30%  brown  rot;  1-1,000%,  100%  brown  rot;  check,  100% 
brown  rot. 

Experiment  II-10B;  January,  1906.  Same  as  last.  Good  lemons 
soaked  twenty-two  hours.  1-200%  permanganate,  no  decay;  1-300%, 
no  decay;  1-400%,  56%  brown  rot;  check,  94%  brown  rot. 

Experiment  11-12 ;  January,  1906.  Soaked  lemons  in  plain  water, 
with  following  strengths  of  permanganate,  to  test  staining  properties: 
Soaked  for  one-half  hour,  or  about  maximum  time  that  fruit  would 
remain  in  the  washer;  1-25%,  a  little  staining;  1-50%,  no  stain; 
1-100% ,  no  stain. 


Bulletin  190.  BROWN  ROT  OF  the  lemon.  67 

Experiment  IV- 1 ;  March,  1906.  Infected  washer  with  a  bucket  of 
orchard  soil,  then  ran  through  26  boxes  of  lemons ;  991  original  brown 
rots  developed  in  these.  (Fig.  25.)  Soaked  50  lemons  in  a  bucketful 
of  this  water  for  two  hours ;  all  developed  brown  rot.  Then  put  per- 
manganate into  the  same  water  in  the  washer  to  make  1-125%  ;  ran 
through  another  25  boxes;  1  lemon  developed  brown  rot.  (Fig.  26.) 
Soaked  50  in  a  bucketful  of  this  water  for  two  hours ;  no  decay. 

Experiment  IV-18 ;  May,  1906.  Like  last.  Washed  6  boxes  in 
infected  water;  122  brown  rots  developed.  Then  added  permanganate 
to  make  1-125%,  and  washed  10  boxes  more;  8  brown  rots  developed. 
Then  added  more  permanganate  to  same  wrater  to  make  1-40%,  and 
washed  10  boxes  more;  no  brown  rot  developed. 

Experiment  IV-27  ;  May,  1906.  Added  two  double  "  handfuls  .  of 
infected  soil  to  a  number  of  buckets  of  water.  In  A,  soaked  50  good 
lemons  three  hours,  with  no  disinfectant;  all  developed  brown  rot. 
In  B,  made  1-200%  permanganate,  14%  brown  rot.  In  C,  1-100% 
permanganate,  30%  brown  rot.  In  D,  1-50%  permanganate,  2%  browrn 
rot  (1  lemon).  The  large  amount  of  dirt  in  these  buckets  seemed  to 
weaken  the  disinfectant. 

Experiment  V-9;  June,  1906.  Infected  buckets  of  water  with  soil 
and  soaked  good  lemons  as  folkws :  Check,  no  disinfectant,  88%  brown 
rot;  permanganate,  1-100%,  1-75%,  1-50%,  and  1-25%,  no  decay. 

Water  Disinfection  With  Copper  Sulphate. 

Experiment  1-52 ;  August,  1905.  Infected  two  buckets  of  water 
with  affected  lemons.  Soaked  50  good  lemons  in  each  over  night,  as 
follows:  Copper  sulphate,  1-20%,  no  decay,  quite  badly  burned;  check, 
no  disinfectant,  all  brown  rot. 

Experiment  1-53 ;  August,  1905.  Soaked  good  lemons  in  infected 
water  for  fourteen  hours,  then  divided  them  into  six  lots  and  soaked 
in  1-20%  copper  sulphate  for  periods  varying  from  one-half  hour  to 
ten  hours;  brown  rot  developed  in  all,  averaging  60%. 

Experiment  1-59;  August,  1905.  Infected  three  buckets  of  water 
with  affected  lemons.  Soaked  50  good  lemons  in  each  for  five  hours, 
writh  following:  1-25%  copper  sulphate,  no  decay  or  injury;  1-50%, 
same  result;  check,  no  disinfectant,  56%  brown  rot. 

Experiment  1-84;  September,  1905.  Infected  four  buckets  of  water, 
and  soaked  good  lemons  over  night.  1-500%  copper  sulphate,  16% 
brown  rot ;  1-1,000%  copper  sulphate,  24%  brown  rot ;  1-4,000%  copper 
sulphate,  48%  brown  rot;  check,  no  disinfectant,  92%  brown  rot.  (See 
further  data  of  this  experiment  under  "Retarding  of  Infection.") 
6— bul.  190 


UNIVERSITY  OF  CALIFORNIA — EXPERIMENT   STATION. 

Experiment  1-88;  September,  1905.  As  last.  1-2,500%  copper  sul- 
phate gave  36%  brown  rot;  1-5,000%  gave  32%  brown  rot;  1-10,000% 
gave  68%  brown  rot;  check,  no  disinfectant,  gave  100%  brown  rot. 
(See  also  under  " Retarding  of  Infection.") 

Experiment  1-103 ;  September,  1905.  As  last.  1-50%  copper  sulphate 
gave  no  brown  rot;  1-100%  and  1-200%,  same;  check,  28%  brown  rot. 

Experiment  1-105 ;  September,  1905.  Same  as  last,  but  infection 
from  soil:  Copper  sulphate,  1-50%,  1-100%,  and  1-200%  gave  no  brown 
rot;  check,  100%  brown  rot. 

Experiment  II-4;  July,  1905.  Soaked  lemons  in  following  solutions 
for  fourteen  to  sixteen  hours:  1  1-4%  copper  sulphate,  fruit  badly 
burned,  2%  blue  mould;  5-8%  copper  sulphate,  badly  burned,  2%  blue 
mould. 

Experiment  II-10B ;  January,  1906.  Soaked  good  lemons  in  infected 
water  as  follows:  1-200%  copper  sulphate,  no  decay;  1-300%  copper 
sulphate,  no  decay;  1-400%  copper  sulphate,  no  decay;  1-1,000%  copper 
sulphate,  2%  brown  rot;  check,  no  disinfectant,  94%  brown  rot. 

Experiment  IV-11 ;  April,  1906.  Infected  washer  with  orchard  soil ; 
ran  through  10  boxes  of  lemons;  380  original  brown  rots  developed. 
Soaked  50  lemons  in  bucket  of  same  water  for  three  hours ;  all  developed 
brown  rot.  Then  added  copper  sulphate  to  same  water  in  washer  to 
make  1-500%  ;  washed  10  boxes  more;  53  brown  rots  developed.  Soaked 
50  lemons  in  bucket  of  same  water  for  three  hours ;  no  decay.  Then 
added  more  copper  sulphate  to  same  water  in  washer  to  make  1-125  ,  ; 
washed  10  boxes  more;  5  brown  rots  developed.  Soaked  50  lemons  in 
bucket  of  same  water  for  three  hours;  no  decay. 

Experiment  IV-22;  May,  1906.  Same  as  last.  Infected  water  and 
washed  6  boxes ;  81  brown  rots  developed.  Then  added  copper  sulphate 
to  make  1-125%,  and  ran  through  10  boxes  more;  no  decay.  Added 
more  copper  sulphate  to  make  1-40%,  and  washed  10  boxes  more;  no 
decay. 

Experiment  IV-27 ;  May,  1906.  Infected  buckets  of  water  with  two 
double  handfuls  of  soil.  Soaked  lemons  as  follows:  1-200%  copper 
sulphate,  2%  brown  rot;  1-100%  and  1-50%  copper  sulphate,  no  decay. 
(See  experiment  of  same  number  under  permanganate.) 

Experiment  V-l;  June,  1906.  Test  of  copper  sulphate  in  infected 
water:  1-100%,  1-75%,  1-50%,  and  1-25%  gave  no  decay.  Check.  100% 
brown   rot. 


Bulletin  190.  BROWN  ROT  OP  THE  LEMON.  69 

Experiments  With  Various  Disinfectants  in  Water. 

Experiment  II-7;  December,  1905.  Infected  buckets  of  water  with 
affected  lemons,  and  soaked  good  lemons  twenty-two  hours:  1-200% 
boric  acid  gave  94%  brown  rot;  1-500%  same  gave  88%  brown  rot; 
1-1,000%  same  gave  90%  brown  rot;  1-200%  salicylic  acid  gave  70% 
brown  rot;  1-500%  same  gave  100%  brown  rot;  1-1,000%  same  gave 
60%  brown  rot. 

The  water  with  which  these  experiments  were  started  was  quite  cold, 
and  did  not  fully  dissolve  the  boric  and  salicylic  acids.  This  is,  there- 
fore, not  an  accurate  test  of  these  substances. 

Experiment  II-10B ;  January,  1906.  As  above,  with  sulphide  of 
potash:  1-100%  and  1-200%  gave  no  decay;  check,  without  disinfectant, 
gave  94%  brown  rot. 

Test  of  Disinfection  of  Washer. 

Experiment  11-16;  May,  1906.  On  the  afternoon  of  May  3d  the 
washer  in  a  packing  house  was  running  with  about  1-150%  permanga- 
nate; next  day,  May  4th,  washed  with  1-75%  permanganate.  Fruit 
from  a  very  badly  affected  orchard.  Soaked  50  good  lemons  in  each  of 
the  following: 

Sediment  of  May  3d  and  plain  water :  44%  brown  rot  developed. 

Sediment  of  May  3d  and  wash  water  of  May  4th :  14%  brown  rot. 

Wash  water  of  May  3d:  10%  brown  rot. 

Mixture  of  three  fourths  of  wash  water  of  May  3d  and  one  fourth 
of  May  4th:  no  decay. 

Wash  water  of  May  4th:  2%  brown  rot. 

Plain  water:  no  decay. 

Sunken  lemons  of  May  3d  (75)  :  all  developed  brown  rot. 

Sunken  lemons  of  May  7th  (after  running  all  day  with  1-75%  per- 
manganate) :  19  out  of  21  developed  brown  rot. 

Experiments  Showing  Retarding  of  Infection  by  Incomplete 

Disinfection. 
Experiments  1-84  and  1-88;  September,  1905.     Soaked  good  lemons 
in  infected  water,  with  following  solutions.     Brown  rot  developed  as 
follows,  the  numbers  denoting  the  number  of  affected  lemons  which 
showed  on  the  different  dates  in  the  different  lots : 

Sept.  12.  Sept.  14.  Sept.  18.  Sept.  20.  Sept  25.  Total. 

Copper   sulphate   1-500% None  None  2              11  16% 

Copper  sulphate   1-1,000% None  None  2              2  2  24% 

Copper  sulphate   1-2,500% None  None  8  None  1  36% 

Copper  sulphate   1-4.000% 5              2  3              1  1  48% 

Copper  sulphate   1-5,000% None           3  4  None  1  32% 

Copper  sulphate   1-10,000% Signs           8  7              2  None  68% 

Check     8            14  1  None  None  92% 

Check     Signs        24  None           1  . .  100% 


'^  UNIVERSITY  OF  CALIFORNIA — EXPERIMENT   STATION. 


DIRECTIONS   FOR   BROWN-ROT   CONTROL. 

1.  Plant  a  cover  crop  in  the  orchard  in  September  or  early  October, 
so  that  a  thick,  continuous  covering  will  be  formed  as  early  as  Jan- 
uary. Yetch  and  bur-clover  are  recommended  for  this  purpose.  S 
well  under  the  trees,  and  furrow  for  irrigation.  Where  a  leguminous 
crop  can  not  be  grown  in  time  to  assist  in  checking  brown  rot,  a  sowing 
of  barley  will  be  found  useful. 

2.  Toward  the  end  of  the  rainy  season  plow-in  the  cover  crop,  and 
begin  the  work  of  cultivation  before  the  ground  becomes  hardened. 
The  orchard  should  be  cultivated  at  frequent  intervals  throughout  the 
summer,  especially  under  the  trees.  To  accomplish  this  the  trees  had 
best  be  pruned  up,  at  least  until  the  bottom  fruit  just  touches  the 
ground,  when  the  soil  underneath  may  be  satisfactorily  stirred.  In 
bad  cases  hand  work  may  be  necessary  at  first. 

3.  In  the  season  of  brown-rot  infection  (from  about  January 
until  early  summer)  disinfect  the  wash  water  by  adding  one  of  the 
following  substances.  Proportions  given  are  for  a  one-thousand-gallon 
tank : 

Formalin — One  and  one  half  pints  in  the  morning,  one  pint  after  noon  in 'the  same 
water. 

Permanganate  of  Potash — One  pound  in  the  morning,  eight  ounces  after  noon  in 
the  same  water. 

Bluestone — Same  as  for  Permanganate. 

The  last  named  is  the  best  substance  for-  the  purpose,  and  may  be 
kept  in  a  stock  solution  of  two  pounds  to  the  gallon.  As  bluestone  will 
slightly  corrode  iron,  tanks  of  this  metal  should  be  kept  painted  with 
asphalt  paint. 

4.  Lemons  infected  in  the  orchard  should  be  carefully  eliminated 
during  the  process  of  picking  and  washing. 

5.  Keep  a  sharp  lookout  for  any  possible  cases  of  rot  in  the  curing 
tents.  Affected  boxes  should  be  carefully  picked  over,  the  rotting 
lemons  thrown  out,  and  those  lying  in  contact  with  them  put  by  them- 
selves for  further  inspection. 


STATION   PUBLICATIONS.  71 


STATION  PUBLICATIONS  AVAILABLE  FOR  DISTRIBUTION. 


REPORTS. 

189G.     Report    of    the    Viticultural    Work    during    the    seasons    1887-93,    with    data 
regarding-  the  Vintages  of  1894-95. 

1897.  Resistant    Vines,    their    Selection,    Adaptation,    and    Grafting.      Appendix    to 

Viticultural  Report  for  1896. 

1898.  Partial   Report  of  Work  of  Agricultural   Experiment   Station   for   the   years 

1895-96  and  1890-97. 
1900.     Report  of  the  Agricultural  Experiment  Station  for  the  year  1897-98. 

1902.  Report  of  the  Agricultural  Experiment  Station  for  1898-1901. 

1903.  Report  of  the  Agricultural  Experiment  Station  for  1901-1903. 

1904.  Twenty-second  Report  of  the  Agricultural  Experiment  Station  for  1903-1904. 

TECHNICAL   BULLETINS—ENTOMOLOGICAL  SERIES. 

Vol.  1,  No.  1 — Wing  Veins  of  Insects. 

No.  2 — Catalogue  of  the  Ephydridae. 

BULLETINS. 

Reprint.  Endurance  of  Drought  in  Soils  of  the  Arid  Region. 

No.  128.  Nature,  Value  and  Utilization  of  Alkali  Lands,  and  Tolerance  of  Alkali. 
(Revised  and  Reprint,  1905.) 

133.  Tolerance  of  Alkali  by  Various  Cultures. 

140.  Lands  of  the  Colorado  Delta  in  Salton  Basin,  and  Supplement. 

141.  Deciduous  Fruits  at  Paso  Robles. 

142.  Grasshoppers  in  California. 

147.  Culture  Work  of  the  Substations. 

148.  Resistant  Vines  and  their  Hybrids. 

149.  California  Sugar  Industry. 

150.  The  Value  of  Oak  Leaves  for  Forage. 

151.  Arsenical  Insecticides. 

152.  Fumigation  Dosage. 

153.  Spraying  with  Distillates. 

154.  Sulfur  Sprays  for  Red  Spider. 

156.  Fowl  Cholera.  1 

158.  California  Olive  Oil;  its  Manufacture. 

159.  Contribution  to  the  Study  of  Fermentation. 

160.  The  Hop  Aphis. 

161.  Tuberculosis  in  Fowls.      (Reprint.) 

162.  Commercial  Fertilizers.      (Dec.  1,  1904.)  * 

163.  Pear  Scab.  ? 

164.  Poultry  Feeding  and  Proprietary  Foods.      (Reprint.) 

165.  Asparagus  and  Asparagus  Rust  in  California. 

166.  Spraying  for  Scale  Insects. 

167.  Manufacture  of  Dry  Wines  in  Hot  Countries. 

168.  Observations  on  Some  Vine  Diseases  in  Sonoma  County. 

169.  Tolerance  of  the  Sugar  Beet  for  Alkali. 

170.  Studies  in  Grasshopper  Control. 

171.  Commercial  Fertilizers.      (June  30,  1905.) 

172.  Further  Experience  in  Asparagus  Rust  Control. 

173.  Commercial  Fertilizers.     (December,  1905.) 

174.  A  New  Wine-Cooling  Machine. 

175.  Tomato  Diseases  in  California. 

176.  Sugar  Beets  in  the  San  Joaquin  Valley. 

177.  A  New  Method  of  Making  Dry  Red  Wine. 

178.  Mosquito  Control. 

179.  Commercial  Fertilizers.     (June,  1906.) 

180.  Resistant  Vineyards. 

181.  The  Selection  of  Seed-Wheat. 

182.  Analysis  of  Paris  Green  and  Lead  Arsenate.     Proposed  Insecticide  Law.  . 

183.  The  California  Tussock-moth. 

184.  Report  of  the  Plant  Pathologist  to  July  1,  1906. 

185.  Report  of  Progress  in  Cereal  Investigations. 

186.  The  Oidium  of  the  Vine. 

187.  Commercial   Fertilizers.      (January,   1907.) 

188.  Lining  of  Ditches  and  Reservoirs  to  Prevent  Seepage  and  Losses. 

189.  Commercial  Fertilizers.     (June,  1907.)  ,; 


UNIVERSITY   OF  CALIFORNIA — EXPERIMENT   STATION. 


CIRCULARS. 


/ 


No. 


1. 
2 

4. 
5. 
7. 
9. 

10. 

11. 
12. 
13. 
15. 

16. 
17. 

13. 
19. 
20. 
21. 

22. 


Texas   Fever. 

Blackleg. 

Hog  Cholera. 

Anthrax.  m 

Contagious  Abortion  in  Cows. 

Remedies  for  Insects. 

Asparagus  Rust. 

Reading  Course  in  Economic 

Entomology.      (Revision.) 
Fumigation  Practice. 
Silk  Culture. 

The   Culture   of   the    Sugar   Beet. 
Recent   Problems   in    Agriculture. 
What  a  University  Farm  is  For. 
Notes  on   Seed- Wheat 
Why      Agriculture      Should      Be 
Taught  in   the   Public   Schools. 
Caterpillars  on  Oaks. 
Disinfection   of   Stables. 
Reading  Course  in  Irrigation. 
The  Advancement  of  Agricultural 

Education.  _,. 

Defecation    of    Must    for    White 
Wine. 


No. 


23. 
24. 
25. 

26. 

27. 

28. 

29. 


30. 
31. 


32. 
33. 


Pure   Yeast  in   Wineries. 
Olive   Pickling. 

Suggestions     Regarding     Exam- 
ination of  Lands. 
Selection     and     Preparation     of 

Vine  Cuttings. 
Marly    Subsoils    and    the    Chlo- 
rosis   or    Yellowing   of    Citrus 
Trees. 
A   Preliminary   Progress  Report 
of  Cereal  Investigations,  190o- 
1907. 
Preliminary   Announcement  con- 
cerning Instruction  in  Practi- 
cal     Agriculture      upon      the 
University    Farm,    Davisville, 
Cal. 
White  Fly  in  California. 
The  Agricultural  College  and  Its 
Relationship  to  the  Scheme  of 
National    Education. 
White  Fly  Eradication. 
Packing  Prunes  in  Cans.     Cane 
Sugar   vs.   Beet   Sugar. 


Copies  may  le  had  on  application  to  Dikectob  of  Experiment  Station.  Berkeley.  Cal. 


